The hydrogen sulfide signaling system: changes during aging and the benefits of caloric restriction

Caloric restriction, Sirtuins, and cardiovascular diseases

ABSTRACT

Caloric restriction (CR) is a well-established dietary intervention known to extend healthy lifespan and exert positive effects on aging-related diseases, including cardiovascular conditions. Sirtuins, a family of nicotinamide adenine dinucleotide (NAD + )-dependent histone deacetylases, have emerged as key regulators of cellular metabolism, stress responses, and the aging process, serving as energy status sensors in response to CR. However, the mechanism through which CR regulates Sirtuin function to ameliorate cardiovascular disease remains unclear. This review not only provided an overview of recent research investigating the interplay between Sirtuins and CR, specifically focusing on their potential implications for cardiovascular health, but also provided a comprehensive summary of the benefits of CR for the cardiovascular system mediated directly via Sirtuins. CR has also been shown to have considerable impact on specific metabolic organs, leading to the production of small molecules that enter systemic circulation and subsequently regulate Sirtuin activity within the cardiovascular system. The direct and indirect effects of CR offer a potential mechanism for Sirtuin modulation and subsequent cardiovascular protection. Understanding the interplay between CR and Sirtuins will provide new insights for the development of interventions to prevent and treat cardiovascular diseases.

The Impact of Drugs on Hydrogen Sulfide Homeostasis in Mammals

Mammalian cells and tissues have the capacity to generate hydrogen sulfide gas (H₂S) via catabolic routes involving cysteine metabolism. H₂S acts on cell signaling cascades that are necessary in many biochemical and physiological roles important in the heart, brain, liver, kidney, urogenital tract, and cardiovascular and immune systems of mammals. Diminished levels of this molecule are observed in several pathophysiological conditions including heart disease, diabetes, obesity, and immune function. Interestingly, in the last two decades, it has become apparent that some commonly prescribed pharmacological drugs can impact the expression and activities of enzymes responsible for hydrogen sulfide production in cells and tissues. Therefore, the current review provides an overview of the studies that catalogue key drugs and their impact on hydrogen sulfide production in mammals.

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.

H2S in Critical Illness—A New Horizon for Sodium Thiosulfate?

Ever since the discovery of endogenous H₂S and the identification of its cytoprotective properties, efforts have been made to develop strategies to use H₂S as a therapeutic agent. The ability of H₂S to regulate vascular tone, inflammation, oxidative stress, and apoptosis might be particularly useful in the therapeutic management of critical illness. However, neither the inhalation of gaseous H₂S, nor the administration of inorganic H₂S-releasing salts or slow-releasing H₂S-donors are feasible for clinical use. Na₂S₂O₃ is a clinically approved compound with a good safety profile and is able to release H₂S, in particular under hypoxic conditions. Pre-clinical studies show promise for Na₂S₂O₃ in the acute management of critical illness. A current clinical trial is investigating the therapeutic potential for Na₂S₂O₃ in myocardial infarct. Pre-eclampsia and COVID-19 pneumonia might be relevant targets for future clinical trials.

Reproductive Longevity and Aging: Geroscience Approaches to Maintain Long-Term Ovarian Fitness

Increases in delayed childbearing worldwide have elicited the need for a better understanding of the biological underpinnings and implications of age-related infertility. In women 35 years and older the incidences of infertility, aneuploidy, and birth defects dramatically increase. These outcomes are a result of age-related declines in both ovarian reserve and oocyte quality. In addition to waning reproductive function, the decline in estrogen secretion at menopause contributes to multisystem aging and the initiation of frailty. Both reproductive and hormonal ovarian function are limited by the primordial follicle pool, which is established in utero and declines irreversibly until menopause. Because ovarian function is dependent on the primordial follicle pool, an understanding of the mechanisms that regulate follicular growth and maintenance of the primordial follicle pool is critical for the development of interventions to prolong the reproductive life span. Multiple pathways related to aging and nutrient-sensing converge in the mammalian ovary to regulate quiescence or activation of primordial follicles. The PI3K/PTEN/AKT/FOXO3 and associated TSC/mTOR pathways are central to the regulation of the primordial follicle pool; however, aging-associated systems such as the insulin-like growth factor-1/growth hormone pathway, and transsulfuration/hydrogen sulfide pathways may also play a role. Additionally, sirtuins aid in maintaining developmental metabolic competence and chromosomal integrity of the oocyte. Here we review the pathways that regulate ovarian reserve and oocyte quality, and discuss geroscience interventions that leverage our understanding of these pathways to promote reproductive longevity.

Hypertension and Aging Affect Liver Sulfur Metabolism in Rats

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

Hydrogen sulfide in longevity and pathologies: Inconsistency is malodorous

Hydrogen sulfide (H₂S) is one of the biologically active gases (gasotransmitters), which plays an important role in various physiological processes and aging. Its production in the course of methionine and cysteine catabolism and its degradation are finely balanced, and impairment of H₂S homeostasis is associated with various pathologies. Despite the strong geroprotective action of exogenous H₂S in C. elegans, there are controversial effects of hydrogen sulfide and its donors on longevity in other models, as well as on stress resistance, age-related pathologies and aging processes, including regulation of senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Here we discuss that the translation potential of H₂S as a geroprotective compound is influenced by a multiplicity of its molecular targets, pleiotropic biological effects, and the overlapping ranges of toxic and beneficial doses. We also consider the challenges of the targeted delivery of H₂S at the required dose. Along with this, the complexity of determining the natural levels of H₂S in animal and human organs and their ambiguous correlations with longevity are reviewed.

Endothelium as a Source and Target of H2S to Improve Its Trophism and Function

The vascular endothelium consists of a single layer of squamous endothelial cells (ECs) lining the inner surface of blood vessels. Nowadays, it is no longer considered as a simple barrier between the blood and vessel wall, but a central hub to control blood flow homeostasis and fulfill tissue metabolic demands by furnishing oxygen and nutrients. The endothelium regulates the proper functioning of vessels and microcirculation, in terms of tone control, blood fluidity, and fine tuning of inflammatory and redox reactions within the vessel wall and in surrounding tissues. This multiplicity of effects is due to the ability of ECs to produce, process, and release key modulators. Among these, gasotransmitters such as nitric oxide (NO) and hydrogen sulfide (H₂S) are very active molecules constitutively produced by endotheliocytes for the maintenance and control of vascular physiological functions, while their impairment is responsible for endothelial dysfunction and cardiovascular disorders such as hypertension, atherosclerosis, and impaired wound healing and vascularization due to diabetes, infections, and ischemia. Upregulation of H₂S producing enzymes and administration of H₂S donors can be considered as innovative therapeutic approaches to improve EC biology and function, to revert endothelial dysfunction or to prevent cardiovascular disease progression. This review will focus on the beneficial autocrine/paracrine properties of H₂S on ECs and the state of the art on H₂S potentiating drugs and tools.

Geroprotective potential of genetic and pharmacological interventions to endogenous hydrogen sulfide synthesis in Drosophila melanogaster

Endogenous hydrogen sulfide (H₂S) is a gasotransmitter with a wide range of physiological functions. Aging is accompanied by disruption of H₂S homeostasis, therefore, interventions to the processes of H₂S metabolism to maintain its balance may have geroprotective potential. Here we demonstrated the additive geroprotective effect of combined genetic and pharmacological interventions to the hydrogen sulfide biosynthesis system by overexpression of cystathionine-β-synthase and cystathionine-γ-lyase genes and treatment with precursors of H₂S synthesis cysteine (Cys) and N-acetyl-L-cysteine (NAC). The obtained results suggest that additive effects of genetic and pharmacological interventions to H₂S metabolism may be associated with the complex interaction between beneficial action of H₂S production and prevention of adverse effects of excess H₂S production by Cys and NAC treatment.

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.

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

Altered gene expression of hydrogen sulfide-producing enzymes in the liver and muscles tissues of hyperthyroid rats

Thyroid hormones have a role in the regulation of hydrogen sulfide (H₂ S) biosynthesis. In this study, we determined the effects of hyperthyroidism on H₂ S levels in various tissues and messenger RNA (mRNA) expression of cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST) in the liver and muscles of the rat. Sixteen male Wistar rats were divided into the hyperthyroid and the control groups. Hyperthyroidism was induced by adding l-thyroxine (12 mg/L) to drinking water for a period of 21 days. H₂ S concentrations in serum, liver, aorta, heart, and soleus muscles, as well as mRNA expressions of CBS, CSE, and 3-MST in these tissues were measured at Day 21. Hyperthyroid rats had lower H₂ S levels in the serum compared with controls (14.7 ± 1.4 vs. 25.7 ± 1.6 µmol/L, p < 0.001). Compared with controls, hyperthyroid rats had lower levels of H₂ S in the aorta (89%), heart (80%), and soleus (103%) muscles, but higher levels in the liver (35%). Hyperthyroidism decreased the ratio of CBS/CSE mRNA expression in the liver and the CSE/CBS mRNA expression in the muscles by decreasing CBS levels in liver (34% cf. controls) and CSE levels in the aorta, heart, and soleus muscles (respectively, 51%, 7%, and 52% cf.). In addition, hyperthyroidism decreased the mRNA expression of 3-MST in the liver (51%) and aorta (33%), and increased it in the heart (300%) and soleus muscle (182%). In conclusion, hyperthyroidism increased H₂ S levels in the liver and decreased it in muscles; these effects are at least in part due to increases and decreases in expression of CSE in the liver and muscles, respectively. These data indicate an association between thyroid hormone status and gene expression of the H₂ S-producing enzymes in the rat.

Long-term Dietary Macronutrients and Hepatic Gene Expression in Aging Mice

Nutrition influences both hepatic function and aging, but mechanisms are poorly understood. Here, the effects of lifelong, ad libitum-fed diets varying in macronutrients and energy on hepatic gene expression were studied. Gene expression was measured using Affymetrix mouse arrays in livers of 46 mice aged 15 months fed one of 25 diets varying in protein, carbohydrates, fat, and energy density from 3 weeks of age. Gene expression was almost entirely influenced by protein intake. Carbohydrate and fat intake had few effects on gene expression compared with protein. Pathways and processes associated with protein intake included those involved with mitochondrial function, metabolic signaling (PI3K-Akt, AMPK, mTOR) and metabolism of protein and amino acids. Protein intake had variable effects on genes associated with regulation of longevity and influenced by caloric restriction. Among the genes of interest with expression that were significantly associated with protein intake are Cth, Gls2, Igf1, and Nnmt, which were increased with higher protein intake, and Igf2bp2, Fgf21, Prkab2, and Mtor, which were increased with lower protein intake. Dietary protein has a powerful impact on hepatic gene expression in older mice, with some overlap with genes previously reported to be involved with regulation of longevity or caloric restriction.

Enhancing and Extending Biological Performance and Resilience

Human performance, endurance, and resilience have biological limits that are genetically and epigenetically predetermined but perhaps not yet optimized. There are few systematic, rigorous studies on how to raise these limits and reach the true maxima. Achieving this goal might accelerate translation of the theoretical concepts of conditioning, hormesis, and stress adaptation into technological advancements. In 2017, an Air Force-sponsored conference was held at the University of Massachusetts for discipline experts to display data showing that the amplitude and duration of biological performance might be magnified and to discuss whether there might be harmful consequences of exceeding typical maxima. The charge of the workshop was "to examine and discuss and, if possible, recommend approaches to control and exploit endogenous defense mechanisms to enhance the structure and function of biological tissues." The goal of this white paper is to fulfill and extend this workshop charge. First, a few of the established methods to exploit endogenous defense mechanisms are described, based on workshop presentations. Next, the white paper accomplishes the following goals to provide: (1) synthesis and critical analysis of concepts across some of the published work on endogenous defenses, (2) generation of new ideas on augmenting biological performance and resilience, and (3) specific recommendations for researchers to not only examine a wider range of stimulus doses but to also systematically modify the temporal dimension in stimulus inputs (timing, number, frequency, and duration of exposures) and in measurement outputs (interval until assay end point, and lifespan). Thus, a path forward is proposed for researchers hoping to optimize protocols that support human health and longevity, whether in civilians, soldiers, athletes, or the elderly patients. The long-term goal of these specific recommendations is to accelerate the discovery of practical methods to conquer what were once considered intractable constraints on performance maxima.

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.

Is there a role of H2S in mediating health span benefits of caloric restriction?

Caloric restriction (CR) is a dietary regimen that aims to reduce the intake of total calories while maintaining adequate supply of key nutrients so as to avoid malnutrition. CR is one of only a small number of interventions that show promising outcomes on health span and lifespan across different species. There is growing interest in the development of compounds that might replicate CR-related benefits without actually restricting food intake. Hydrogen sulfide (H₂S) is produced inside the bodies of many animals, including humans, by evolutionarily conserved H₂S synthesizing enzymes. Endogenous H₂S is increasingly recognized as an important gaseous signalling molecule involved in diverse cellular and molecular processes. However, the specific role of H₂S in diverse biological processes remains to be elucidated and not all its biological effects are beneficial. Nonetheless, recent evidence suggests that the biological functions of H₂S intersect with the network of evolutionarily conserved nutrient sensing and stress response pathways that govern organismal responses to CR. Induction of H₂S synthesizing enzymes appears to be a conserved and essential feature of the CR response in evolutionarily distant organisms, including nematodes and mice. Here we review the evidence for a role of H₂S in CR and lifespan modulation. H₂S releasing drugs, capable of controlled delivery of exogenous H₂S, are currently in clinical development. These findings suggest such H₂S releasing drugs as a promising novel avenue for the development of CR mimetic compounds.

The role of hydrogen sulfide in aging and age-related pathologies

When humans grow older, they experience inevitable and progressive loss of physiological function, ultimately leading to death. Research on aging largely focuses on the identification of mechanisms involved in the aging process. Several proposed aging theories were recently combined as the 'hallmarks of aging'. These hallmarks describe (patho-)physiological processes that together, when disrupted, determine the aging phenotype. Sustaining evidence shows a potential role for hydrogen sulfide (H₂S) in the regulation of aging. Nowadays, H₂S is acknowledged as an endogenously produced signaling molecule with various (patho-) physiological effects. H₂S is involved in several diseases including pathologies related to aging. In this review, the known, assumed and hypothetical effects of hydrogen sulfide on the aging process will be discussed by reviewing its actions on the hallmarks of aging and on several age-related pathologies.

Cardiovascular disease and resuscitated septic shock lead to the downregulation of the H2S-producing enzyme cystathionine-γ-lyase in the porcine coronary artery

BACKGROUND

Downregulation of the hydrogen sulfide (H₂S)-producing enzymes cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), and/or 3-mercaptopyruvate sulfurtransferase (3-MST) is associated with chronic cardiovascular pathologies. Nevertheless, equivocal data are available on both the expression and function of these enzymes in coronary arteries (CA). We recently reported that atherosclerotic pigs subjected to sepsis developed impaired cardiac function, which coincided with decreased myocardial CSE expression and increased nitrotyrosine formation. To define the endogenous source(s) of H₂S in the CA, we studied the expression of CBS, CSE, or 3-MST in the CA of pigs subjected to septic shock with/without pre-existing cardiovascular co-morbidity.

METHODS

Anesthetized and instrumented FBM "familial hypercholesterolemia Bretoncelles Meishan" pigs with high-fat diet-induced hypercholesterolemia and atherosclerosis were subjected to polymicrobial septic shock, or sham procedure, and subsequent intensive care therapy for 24 h. Young German domestic pigs were used as naïve controls. CSE, CBS, 3-MST, HO-1, eNOS, and nitrotyrosine expression was quantified by immunohistochemistry of formalin-fixed paraffin sections.

RESULTS

FBM pigs, in the absence of septic shock, showed decreased CSE expression in the media. This decrease became more pronounced after sepsis. The expression pattern of HO-1 resembled the pattern of CSE expression. CBS protein was not detected in the media of any of the CA examined but was localized to the adventitia and only in the atheromatous plaques containing foam cells of the CA, in regions that also displayed abundant nitrotyrosine formation. The CBS expression in the adventitia was not associated with nitrotyrosine formation. 3-MST expression was not found in any of the CA samples.

CONCLUSIONS

We hypothesize that (i) the reduced CSE expression in FBM pigs may contribute to their cardiovascular disease phenotype and moreover (ii) the further decrease in CA CSE expression in sepsis may contribute to the sepsis-associated cardiac dysfunction.

Proteomics-Based Identification of the Molecular Signatures of Liver Tissues from Aged Rats following Eight Weeks of Medium-Intensity Exercise

Physical activity has emerged as a powerful intervention that promotes healthy aging by maintaining the functional capacity of critical organ systems. Here, by combining functional and proteomics analyses, we examined how hepatic phenotypes might respond to exercise treatment in aged rats. 16 male aged (20 months old) SD rats were divided into exercise and parallel control groups at random; the exercise group had 8 weeks of treadmill training with medium intensity. Whole protein samples of the liver were extracted from both groups and separated by two-dimensional gel electrophoresis. Alternatively objective protein spots with >2-fold difference in expression were selected for enzymological extraction and MS/MS identification. Results show increased activity of the manganese superoxide dismutase and elevated glutathione levels in the livers of exercise-treated animals, but malondialdehyde contents obviously decreased in the liver of the exercise group. Proteomics-based identification of differentially expressed proteins provided an integrated view of the metabolic adaptations occurring in the liver proteome during exercise, which significantly altered the expression of several proteins involved in key liver metabolic pathways including mitochondrial sulfur, glycolysis, methionine, and protein metabolism. These findings indicate that exercise may be beneficial to aged rats through modulation of hepatic protein expression profiles.

Hydrogen sulphide in cardiovascular system: A cascade from interaction between sulphur atoms and signalling molecules

As a gasotransmitter, hydrogen sulphide exerts its extensive physiological and pathophysiological effects in mammals. The interaction between sulphur atoms and signalling molecules forms a cascade that modulates cellular functions and homeostasis. In this review, we focus on the signalling mechanism underlying the effect of hydrogen sulphide in the cardiovascular system and metabolism as well as the biological relevance to human diseases.

Integromics network meta-analysis on cardiac aging offers robust multi-layer modular signatures and reveals micronome synergism

Background

The avalanche of integromics and panomics approaches shifted the deciphering of aging mechanisms from single molecular entities to communities of them. In this orientation, we explore the cardiac aging mechanisms – risk factor for multiple cardiovascular diseases - by capturing the micronome synergism and detecting longevity signatures in the form of communities (modules).

For this, we developed a meta-analysis scheme that integrates transcriptome expression data from multiple cardiac-specific independent studies in mouse and human along with proteome and micronome interaction data in the form of multiple independent weighted networks. Modularization of each weighted network produced modules, which in turn were further analyzed so as to define consensus modules across datasets that change substantially during lifespan. Also, we established a metric that determines - from the modular perspective - the synergism of microRNA-microRNA interactions as defined by significantly functionally associated targets.

Results

The meta-analysis provided 40 consensus integromics modules across mouse datasets and revealed microRNA relations with substantial collective action during aging. Three modules were reproducible, based on homology, when mapped against human-derived modules. The respective homologs mainly represent NADH dehydrogenases, ATP synthases, cytochrome oxidases, Ras GTPases and ribosomal proteins. Among various observations, we corroborate to the involvement of miR-34a (included in consensus modules) as proposed recently; yet we report that has no synergistic effect. Moving forward, we determined its age-related neighborhood in which HCN3, a known heart pacemaker channel, was included. Also, miR-125a-5p/-351, miR-200c/-429, miR-106b/-17, miR-363/-92b, miR-181b/-181d, miR-19a/-19b, let-7d/-7f, miR-18a/-18b, miR-128/-27b and miR-106a/-291a-3p pairs exhibited significant synergy and their association to aging and/or cardiovascular diseases is supported in many cases by a disease database and previous studies. On the contrary, we suggest that miR-22 has not substantial impact on heart longevity as proposed recently.

Conclusions

We revised several proteins and microRNAs recently implicated in cardiac aging and proposed for the first time modules as signatures. The integromics meta-analysis approach can serve as an efficient subvening signature tool for more-oriented better-designed experiments. It can also promote the combinational multi-target microRNA therapy of age-related cardiovascular diseases along the continuum from prevention to detection, diagnosis, treatment and outcome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1256-3) contains supplementary material, which is available to authorized users.

Endogenous hydrogen sulfide production is essential for dietary restriction benefits

Dietary restriction (DR) without malnutrition encompasses numerous regimens with overlapping benefits including longevity and stress resistance, but unifying nutritional and molecular mechanisms remain elusive. In a mouse model of DR-mediated stress resistance, we found that sulfur amino acid (SAA) restriction increased expression of the transsulfuration pathway (TSP) enzyme cystathionine γ-lyase (CGL), resulting in increased hydrogen sulfide (H2S) production and protection from hepatic ischemia reperfusion injury. SAA supplementation, mTORC1 activation, or chemical/genetic CGL inhibition reduced H2S production and blocked DR-mediated stress resistance. In vitro, the mitochondrial protein SQR was required for H2S-mediated protection during nutrient/oxygen deprivation. Finally, TSP-dependent H2S production was observed in yeast, worm, fruit fly, and rodent models of DR-mediated longevity. Together, these data are consistent with evolutionary conservation of TSP-mediated H2S as a mediator of DR benefits with broad implications for clinical translation. PAPERFLICK:

GYY4137, a novel water-soluble, H2S-releasing molecule

Hydrogen sulfide (H2S) is now recognized as the so called "third gasotransmitter" taking its place alongside nitric oxide and carbon monoxide. In recent years, H2S has been reported to exhibit a diverse range of pharmacological effects in biological systems. Much of this evidence is derived from a combination of conventional pharmacological and genetic approaches coupled with the use of chemical compounds such as sodium hydrosulfide, a rapid H2S releasing donor. Developments in the design of new drug entities which attempt to take into account physicochemical properties, targeting to specific cellular organelles, triggering of H2S release upon specific chemical reactions in the cell, and controlling the release of H2S over extended periods of time have been described. For most of these molecules, little or no work has been conducted to determine their biological activity or possible therapeutic effects. It is therefore not clear whether such molecules have therapeutic potential which highlights the need for further in vivo studies. One exception to the general rule is GYY4137 (morpholin-4-ium 4-methoxyphenyl(morpholino) phosphinodithioate), a slow releasing H2S donor, which has been evaluated for activity in a range of pharmacological models both in vitro and in vivo. GYY4137 was first reported to release H2S and exhibit vasodilator activity over 5 years ago and, to date, GYY4137 is becoming increasingly employed as a pharmacological "tool" to explore the biological functions of H2S.

H2S and Blood Vessels: An Overview

The physiological and biomedical importance of hydrogen sulfide (H2S) has been fully recognized in the cardiovascular system as well as in the rest of the body. In blood vessels, cystathionine γ-lyase (CSE) is a major H2S-producing enzyme expressed in both smooth muscle and endothelium as well as periadventitial adipose tissues. Regulation of H2S production from CSE is controlled by a complex integration of transcriptional, posttranscriptional, and posttranslational mechanisms in blood vessels. In smooth muscle cells, H2S regulates cell apoptosis, phenotypic switch, relaxation and contraction, and calcification. In endothelial cells, H2S controls cell proliferation, cellular senescence, oxidative stress, inflammation, etc. H2S interacts with nitric oxide and acts as an endothelium-derived relaxing factor and an endothelium-derived hyperpolarizing factor. H2S generated from periadventitial adipose tissues acts as an adipocyte-derived relaxing factor and modulates the vascular tone. Extensive evidence has demonstrated the beneficial roles of the CSE/H2S system in various blood vessel diseases, such as hypertension, atherosclerosis, and aortic aneurysm. The important roles signaling in the cardiovascular system merit further intensive and extensive investigation. H2S-releasing agents and CSE activators will find their great applications in the prevention and treatment of blood vessel-related disorders.

H2S: A New Approach to Lifespan Enhancement and Healthy Ageing?

Ageing, a progressive structural and functional decline, is considered to be a major risk factor for virtually all ageing-associated pathologies and disabilities, including Alzheimer's disease, Parkinson's disease, stroke, diabetes, atherosclerosis and certain cancers. Biogerontology research has now been largely directed towards finding novel drug targets to decelerate the ageing process and attain healthy ageing in order to delay the onset of all ageing-related diseases. H2S has been reported to exert vasodilatory, antioxidant, antiapoptotic and anti-inflammatory actions and has been shown to act as a signalling molecule, neuromodulator and cytoprotectant. Intriguingly, H2S has been reported to regulate cell cycle and survival in healthy cells which suggests that it may regulate cell fate and hence the ageing process. This chapter sets out to provide an overview of the current knowledge regarding the involvement of H2S in ageing, with a specific focus on the invertebrate model nematode C. elegans.

Phosphinodithioate and Phosphoramidodithioate Hydrogen Sulfide Donors

Hydrogen sulfide is rapidly emerging as a key physiological mediator and potential therapeutic tool in numerous areas such as acute and chronic inflammation, neurodegenerative and cardiovascular disease, diabetes, obesity and cancer. However, the vast majority of the published studies have employed crude sulfide salts such as sodium hydrosulfide (NaSH) and sodium sulfide (Na2S) as H2S "donors" to generate H2S. Although these salts are cheap, readily available and easy to use, H2S generated from them occurs as an instantaneous and pH-dependent dissociation, whereas endogenous H2S synthesis from the enzymes cystathionine γ-lyase, cystathionine-β-synthase and 3-mercaptopyruvate sulfurtransferase is a slow and sustained process. Furthermore, sulfide salts are frequently used at concentrations (e.g. 100 μM to 10 mM) far in excess of the levels of H2S reported in vivo (nM to low μM). For the therapeutic potential of H2S is to be properly harnessed, pharmacological agents which generate H2S in a physiological manner and deliver physiologically relevant concentrations are needed. The phosphorodithioate GYY4137 has been proposed as "slow-release" H2S donors and has shown promising efficacy in cellular and animal model diseases such as hypertension, sepsis, atherosclerosis, neonatal lung injury and cancer. However, H2S generation from GYY4137 is inefficient necessitating its use at high concentrations/doses. However, structural modification of the phosphorodithioate core has led to compounds (e.g. AP67 and AP105) with accelerated rates of H2S generation and enhanced biological activity. In this review, the therapeutic potential and limitations of GYY4137 and related phosphorodithioate derivatives are discussed.

Potential of garlic (Allium sativum) in lowering high blood pressure: mechanisms of action and clinical relevance

Garlic supplements have shown promise in the treatment of uncontrolled hypertension, lowering blood pressure (BP) by about 10 mmHg systolic and 8 mmHg diastolic, similar to standard BP medication. Aged garlic extract, which contains S-allylcysteine as the bioactive sulfur compound, in particular is standardizable and highly tolerable, with little or no known harmful interaction when taken with other BP-reducing or blood-thinning medication. Here we describe biologically plausible mechanisms of garlic's BP-lowering effect. Garlic-derived polysulfides stimulate the production of the vascular gasotransmitter hydrogen sulfide (H2S) and enhance the regulation of endothelial nitric oxide (NO), which induce smooth muscle cell relaxation, vasodilation, and BP reduction. Several dietary and genetic factors influence the efficiency of the H2S and NO signaling pathways and may contribute to the development of hypertension. Sulfur deficiency might play a part in the etiology of hypertension, and could be alleviated with supplementation of organosulfur compounds derived from garlic.

H2S during circulatory shock: some unresolved questions

Numerous papers have been published on the role of H2S during circulatory shock. Consequently, knowledge about vascular sulfide concentrations may assume major importance, in particular in the context of "acute on chronic disease", i.e., during circulatory shock in animals with pre-existing chronic disease. This review addresses the questions (i) of the "real" sulfide levels during circulatory shock, and (ii) to which extent injury and pre-existing co-morbidity may affect the expression of H2S producing enzymes under these conditions. In the literature there is a huge range on sulfide blood levels during circulatory shock, in part as a result of the different analytical methods used, but also due to the variable of the models and species studied. Clearly, some of the very high levels reported should be questioned in the context of the well-known H2S toxicity. As long as "real" sulfide levels during circulatory shock are unknown and/or undetectable "on line" due to the lack of appropriate techniques, it appears to be premature to correlate the measured blood levels of hydrogen sulfide with the severity of shock or the H2S therapy-related biological outcomes. The available data on the tissue expression of the H2S-releasing enzymes during circulatory shock suggest that a "constitutive" CSE expression may play a crucial role of for the maintenance of organ function, at least in the kidney. The data also indicate that increased CBS and CSE expression, in particular in the lung and the liver, represents an adaptive response to stress states.

Hydrogen sulfide is an endogenous regulator of aging in Caenorhabditis elegans

AIMS

To investigate the role of endogenous hydrogen sulfide (H2S) in the control of aging and healthspan of Caenorhabditis elegans.

RESULTS

We show that the model organism, C. elegans, synthesizes H2S. Three H2S-synthesizing enzymes are present in C. elegans, namely cystathionine γ lyase (CSE), cystathionine β synthetase, and 3-mercaptopyruvate transferase (MPST or 3-MST). Genetic deficiency of mpst-1 (3-MST orthologue 1), but not cth-2 (CSE orthologue), reduced the lifespan of C. elegans. This effect was reversed by a pharmacological H2S donor (GYY4137). GYY4137 also reduced detrimental age-dependent changes in a range of physiological indices, including pharyngeal contraction and defecation. Treatment of C. elegans with GYY4137 increased the expression of several age-related, stress response, and antioxidant genes, whereas MitoSOX Red fluorescence, indicative of reactive oxygen species generation, was increased in mpst-1 knockouts and decreased by GYY4137 treatment. GYY4137 additionally increased the lifespan in short-lived mev-1 mutants with elevated oxidative stress and protected wild-type C. elegans against paraquat poisoning. The lifespan-prolonging and health-promoting effects of H2S in C. elegans are likely due to the antioxidant action of this highly cell-permeable gas.

INNOVATION

The possibility that novel pharmacological agents based on the principle of H2S donation may be able to retard the onset of age-related disease by slowing the aging process warrants further study.

CONCLUSION

Our results show that H2S is an endogenous regulator of oxidative damage, metabolism, and aging in C. elegans and provide new insight into the mechanisms, which control aging in this model organism.

Hydrogen sulfide protects against cellular senescence via S-sulfhydration of Keap1 and activation of Nrf2

AIMS

H2S, a third member of gasotransmitter family along with nitric oxide and carbon monoxide, exerts a wide range of cellular and molecular actions in our body. Cystathionine gamma-lyase (CSE) is a major H2S-generating enzyme in our body. Aging at the cellular level, known as cellular senescence, can result from increases in oxidative stress. The aim of this study was to investigate how H2S attenuates oxidative stress and delays cellular senescence.

RESULTS

Here we showed that mouse embryonic fibroblasts isolated from CSE knockout mice (CSE KO-MEFs) display increased oxidative stress and accelerated cellular senescence in comparison with MEFs from wild-type mice (WT-MEFs). The protein expression of p53 and p21 was significantly increased in KO-MEFs, and knockdown of p53 or p21 reversed CSE deficiency-induced senescence. Incubation of the cells with NaHS (a H2S donor) significantly increased the glutathione (GSH) level and rescued KO-MEFs from senescence. Nrf2 is a master regulator of the antioxidant response, and Keap1 acts as a negative regulator of Nrf2. NaHS S-sulfhydrated Keap1 at cysteine-151, induced Nrf2 dissociation from Keap1, enhanced Nrf2 nuclear translocation, and stimulated mRNA expression of Nrf2-targeted downstream genes, such as glutamate-cysteine ligase and GSH reductase.

INNOVATION

These results provide a mechanistic insight into how H2S signaling mediates cellular senescence induced by oxidative stress.

CONCLUSION

H2S protects against cellular aging via S-sulfhydration of Keap1 and Nrf2 activation in association with oxidative stress.

Hydrogen sulfide, the next potent preventive and therapeutic agent in aging and age-associated diseases

Hydrogen sulfide (H(2)S) is the third endogenous signaling gasotransmitter, following nitric oxide and carbon monoxide. It is physiologically generated by cystathionine-γ-lyase, cystathionine-β-synthase, and 3-mercaptopyruvate sulfurtransferase. H(2)S has been gaining increasing attention as an important endogenous signaling molecule because of its significant effects on the cardiovascular and nervous systems. Substantial evidence shows that H(2)S is involved in aging by inhibiting free-radical reactions, activating SIRT1, and probably interacting with the age-related gene Klotho. Moreover, H(2)S has been shown to have therapeutic potential in age-associated diseases. This article provides an overview of the physiological functions and effects of H(2)S in aging and age-associated diseases, and proposes the potential health and therapeutic benefits of H(2)S.

Hydrogen sulfide-mediated myocardial pre- and post-conditioning

Coronary artery disease is a major cause of morbidity and mortality in the Western world. Acute myocardial infarction, resulting from coronary artery atherosclerosis, is a serious and often fatal consequence of coronary artery disease, resulting in cell death in the myocardium. Pre- and post-conditioning of the myocardium are two treatment strategies that reduce the amount of cell death significantly. Hydrogen sulfide has recently been identified as a potent cardioprotective signaling molecule, which is a highly effective pre- and post-conditioning agent. The cardioprotective signaling pathways involved in hydrogen sulfide-based pre- and post-conditioning will be explored in this article.

Hydrogen sulfide in the pathogenesis of atherosclerosis and its therapeutic potential

Hydrogen sulfide (H(2)S) was the third gaseous transmitter to be discovered, along with nitric oxide and carbon monoxide, and has been proposed to be involved in numerous physiological processes and pathology of various diseases. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease, including atherosclerosis. Atherosclerosis is characterized by multiple key events including endothelial dysfunction, monocyte infiltration and their differentiation into macrophages, conversion of lesion-resident macrophages into foam cells, and smooth muscle cell proliferation. Increasing evidence has indicated that H(2)S plays a potentially significant role in all of these biological processes and that malfunction of H(2)S homeostasis may contribute to the pathogenesis of atherosclerosis. Experiments have demonstrated that H(2)S supplementation ameliorated many of these atherogenic processes and hence, such supplementation potentially may prove to be of therapeutic benefit in the prevention or treatment of atherosclerosis. H(2)S levels may be induced by the administration of H(2)S or H(2)S donors, or alternatively be reduced by the administration of specific cystathionine β-synthase or cystathionine γ-lyase inhibitors. However, issues remain with the potential use of currently available H(2)S-modulating agents in a clinical setting. This review will provide a description of the current literature on the involvement of H(2)S in these key aspects of vascular biology that contribute to the development of atherosclerosis, as well as the therapeutic potential of currently available H(2)S-modulating agents.

Hydrogen sulfide-mediated cardioprotection: mechanisms and therapeutic potential

H2S (hydrogen sulfide), viewed with dread for more than 300 years, is rapidly becoming a ubiquitously present and physiologically relevant signalling molecule. Knowledge of the production and metabolism of H2S has spurred interest in delineating its functions both in physiology and pathophysiology of disease. Although its role in blood pressure regulation and interaction with NO is controversial, H2S, through its anti-apoptotic, anti-inflammatory and antioxidant effects, has demonstrated significant cardioprotection. As a result, a number of sulfide-donor drugs, including garlic-derived polysulfides, are currently being designed and investigated for the treatment of cardiovascular conditions, specifically myocardial ischaemic disease. However, huge gaps remain in our knowledge about this gasotransmitter. Only by additional studies will we understand more about the role of this intriguing molecule in the treatment of cardiovascular disease.