The Role of Hydrogen Sulfide on Cardiovascular Homeostasis: An Overview with Update on Immunomodulation

Discovery of New Schiff Bases Tethered Pyrazole Moiety: Design, Synthesis, Biological Evaluation, and Molecular Docking Study as Dual Targeting DHFR/DNA Gyrase Inhibitors with Immunomodulatory Activity

A series of Bis-pyrazole Schiff bases (6a–d and 7a–d) and mono-pyrazole Schiff bases (8a–d and 9a–d) were designed and synthesized through the reaction of 5-aminopyrazoles 1a–d with aldehydes 2–5 using mild reaction condition with a good yield percentage. The chemical structure of newly formed Schiff bases tethered pyrazole core was confirmed based on spectral and experimental data. All the newly formed pyrazole Schiff bases were evaluated against eight pathogens (Gram-positive, Gram-negative, and fungi). The result exhibited that, most of them have good and broad activities. Among those, only six Schiff bases (6b, 7b, 7c, 8a, 8d, and 9b) displayed MIC values (0.97–62.5 µg/mL) compared to Tetracycline (15.62–62.5 µg/mL) and Amphotericin B (15.62–31.25 µg/mL), MBC values (1.94–87.5 µg/mL) and selectivity to tumor cell than normal cells. Immunomodulatory activities showed that the promising Schiff bases increase the immunomodulator effect of defense cell and the Schiff base 8a is the highest one by (Intra. killing activity = 136.5 ± 0.3%) having a pyrazole moiety as well as amide function (O=C-NH₂) and piperidinyl core. Furthermore, the most potent one exhibited broad activity depending on both MIC and MBC values. Moreover, to study the mechanism of these pyrazole Schiff bases, two active Schiff bases 8a and 9b from six derivatives were introduced to study the enzyme assay as dihydrofolate reductase (DHFR) on E. coli organism and DNA gyrase with two different organisms, S. aureus and B. subtilis, to determine the inhibitory activities with lower values in the case of DNA gyrase (8a and 9b) or nearly as DHFR compound 9b, while pyrazole 8a showed excellent inhibitory against all enzyme assay. The molecular docking study against dihydrofolate reductase and DNA gyrase were performed to study the binding between active site in the pocket with the two Schiff bases (8a and 9b) that exhibited good binding affinity with different bond types as H-bonding, aren-aren, and arene-cation interaction as well as study the physicochemical and pharmacokinetic properties of the two active Schiff bases 8a and 9b.

Effects of drinking natural hydrogen sulfide (H2S) waters: a systematic review of in vivo animal studies

Natural waters containing originally hydrogen sulfide (H2S) gas with an S2-level at least 1 mg/L are classified as "sulfur waters" or "hydrogen sulfide waters." This systematic review aimed to evaluate in vivo experimental studies investigating the biological effects of natural H2S water drinking in healthy or with disease model laboratory animals. A comprehensive databases search (PubMed, Embase, Web of Science, and Google Scholar) was performed and PICOS criteria were used to assess eligibility. All relevant studies were identified, screened, and examined. The qualitative assessment was performed with the help of the SYRCLE Risk of Bias tool. A total of nine articles were included. The extracted data showed that ad libitum drinking of such waters by rats and mice exert beneficial effects on animal model of diabetes and glucose metabolism plus protective effects on diabetic cardiac, testicular, and nephrological complications as shown biochemically, histopathologically, and bio-molecularly. Additional effects were gastroprotection, antioxidant effects and improvement of intestinal physiology in healthy animals, reduction in general signs of murine model of colitis in mice, improvement in lipid metabolism and lipid-lowering effect, and positive interference with the enterohepatic cycle of the bile acids and biliary functions in hyperlipidemic rats. This systematic review provides preliminary insights into the "biological truth" about natural H2S waters and partly elucidates their potential therapeutic role in balneology and health resort medicine. However, it should be kept in mind that the retrieved preclinical data cannot be directly extrapolated to humans. Additionally, most of the included studies were rated for unclear risk of bias across all categories except random allocation, reflecting very poor reporting of methodological details. These limitations should be addressed when planning similar studies in the future. The question "can traditional hydropinic therapies or drinking cures with H2S waters at natural sulfur water spas/health resorts or natural (even artificial) H2S water consumption at home exert similar effects in humans?" remains to be clarified by clinical trials.

The health of communities living in proximity of geothermal plants generating heat and electricity: A review

Since the 1990s, in areas with natural geothermal manifestations studies on the association between exposure to pollutants and health effect have become increasingly relevant. These emissions consist of water vapor mixed with carbon dioxide, hydrogen sulfide (H₂S), methane and, to a lesser extent, rare gases and trace elements in volatile forms. Considering the indications of the World Health Organization and the growth in the use of geothermal energy for energy production, this review aims to report studies exploring the health status of the populations living in areas where geothermal energy is used to produce heat and electricity. Studies on the health effects of the general population exposed to emissions from both natural geothermal events and plants using geothermal energy at domestic or commercial level have been considered between 1999 and 2019. Studies were classified into those based on health indicators and those based on proxy-individual level exposure metrics. Both statistically significant results (p<0.05) and interesting signals were commented. The 19 studies selected (New Zealand, Iceland and Italy) provide heterogeneous results, with an increased risk for several tumor sites. Exposure to H₂S low concentrations is positively associated with an increment of respiratory symptoms, anti-asthma drugs use, mortality for respiratory diseases and lung cancer. Exposure to H₂S high levels is inversely related to cancer mortality but associated with an increase in hospitalization for respiratory diseases, central nervous system disorders and cardiovascular diseases. The results indicate that the health of populations residing in areas rich in geothermal emissions presents some critical elements to be explored. The two major limitations of the studies are the ecological design and the inadequate exposure assessment. The authors suggested the prosecution and the systematization of health surveillance and human biomonitoring activities associated with permanent control of atmospheric emissions from both industrial and natural plants.

Glutathione-Allylsulfur Conjugates as Mesenchymal Stem Cells Stimulating Agents for Potential Applications in Tissue Repair

The endogenous gasotransmitter H₂S plays an important role in the central nervous, respiratory and cardiovascular systems. Accordingly, slow-releasing H₂S donors are powerful tools for basic studies and innovative pharmaco-therapeutic agents for cardiovascular and neurodegenerative diseases. Nonetheless, the effects of H₂S-releasing agents on the growth of stem cells have not been fully investigated. H₂S preconditioning can enhance mesenchymal stem cell survival after post-ischaemic myocardial implantation; therefore, stem cell therapy combined with H₂S may be relevant in cell-based therapy for regenerative medicine. Here, we studied the effects of slow-releasing H₂S agents on the cell growth and differentiation of cardiac Lin⁻ Sca1⁺ human mesenchymal stem cells (cMSC) and on normal human dermal fibroblasts (NHDF). In particular, we investigated the effects of water-soluble GSH–garlic conjugates (GSGa) on cMSC compared to other H₂S-releasing agents, such as Na₂S and GYY4137. GSGa treatment of cMSC and NHDF increased their cell proliferation and migration in a concentration dependent manner with respect to the control. GSGa treatment promoted an upregulation of the expression of proteins involved in oxidative stress protection, cell–cell adhesion and commitment to differentiation. These results highlight the effects of H₂S-natural donors as biochemical factors that promote MSC homing, increasing their safety profile and efficacy after transplantation, and the value of these donors in developing functional 3D-stem cell delivery systems for cardiac muscle tissue repair and regeneration.

Hydrogen Sulfide as a Potential Alternative for the Treatment of Myocardial Fibrosis

Harmful, stressful conditions or events in the cardiovascular system result in cellular damage, inflammation, and fibrosis. Currently, there is no targeted therapy for myocardial fibrosis, which is highly associated with a large number of cardiovascular diseases and can lead to fatal heart failure. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter similar to nitric oxide and carbon monoxide. H₂S is involved in the suppression of oxidative stress, inflammation, and cellular death in the cardiovascular system. The level of H₂S in the body can be boosted by stimulating its synthesis or supplying it exogenously with a simple H₂S donor with a rapid- or slow-releasing mode, an organosulfur compound, or a hybrid with known drugs (e.g., aspirin). Hypertension, myocardial infarction, and inflammation are exaggerated when H₂S is reduced. In addition, the exogenous delivery of H₂S mitigates myocardial fibrosis caused by various pathological conditions, such as a myocardial infarct, hypertension, diabetes, or excessive β-adrenergic stimulation, via its involvement in a variety of signaling pathways. Numerous experimental findings suggest that H₂S may work as a potential alternative for the management of myocardial fibrosis. In this review, the antifibrosis role of H₂S is briefly addressed in order to gain insight into the development of novel strategies for the treatment of myocardial fibrosis.

Role of Endothelial Dysfunction in Cardiovascular Diseases: The Link Between Inflammation and Hydrogen Sulfide

Endothelial cells are important constituents of blood vessels that play critical roles in cardiovascular homeostasis by regulating blood fluidity and fibrinolysis, vascular tone, angiogenesis, monocyte/leukocyte adhesion, and platelet aggregation. The normal vascular endothelium is taken as a gatekeeper of cardiovascular health, whereas abnormality of vascular endothelium is a major contributor to a plethora of cardiovascular ailments, such as atherosclerosis, aging, hypertension, obesity, and diabetes. Endothelial dysfunction is characterized by imbalanced vasodilation and vasoconstriction, elevated reactive oxygen species (ROS), and proinflammatory factors, as well as deficiency of nitric oxide (NO) bioavailability. The occurrence of endothelial dysfunction disrupts the endothelial barrier permeability that is a part of inflammatory response in the development of cardiovascular diseases. As such, abrogation of endothelial cell activation/inflammation is of clinical relevance. Recently, hydrogen sulfide (H₂S), an entry as a gasotransmitter, exerts diverse biological effects through acting on various targeted signaling pathways. Within the cardiovascular system, the formation of H₂S is detected in smooth muscle cells, vascular endothelial cells, and cardiomyocytes. Disrupted H₂S bioavailability is postulated to be a new indicator for endothelial cell inflammation and its associated endothelial dysfunction. In this review, we will summarize recent advances about the roles of H₂S in endothelial cell homeostasis, especially under pathological conditions, and discuss its putative therapeutic applications in endothelial inflammation-associated cardiovascular disorders.

mTORC1-Sch9 regulates hydrogen sulfide production through the transsulfuration pathway

Endogenous hydrogen sulfide mediates anti-aging benefits of dietary restriction (DR). However, it is unclear how H₂S production is regulated by pathways related to DR. Due to the importance of mTORC1 pathway in DR, we investigated the effects of Sch9, a yeast homolog of mammalian S6K1 and a major substrate of mTORC1 on H₂S production in yeast Saccharomyces cerevisiae. We found that inhibition of the mTORC1-Sch9 pathway by SCH9 deletion, rapamycin or myriocin treatment resulted in a dramatic decrease in H₂S production. Although deficiency of SCH9 did not alter the intracellular level of methionine, the intracellular level of cysteine increased in Δsch9 cells. The expression of CYS3 and CYS4, two transsulfuration pathway genes encoding cystathionine gamma-lyase (CGL) and cystathionine beta-synthase (CBS), were also decreased under mTORC1-Sch9 inhibition. Overexpression of CYS3 or CYS4 in Δsch9 cells or WT cells treated with rapamycin rescued the deficiency of H₂S production. Finally, we also observed a reduction in H₂S production and lowering of both mRNA and protein levels of CGL and CBS in cultured human cells treated with rapamycin to reduce mTORC1 pathway activity. Thus, our findings reveal a probably conserved mechanism in which H₂S production by the transsulfuration pathway is regulated by mTORC1-Sch9 signaling.

Sodium hydrosulphide restores tumour necrosis factor-α-induced mitochondrial dysfunction and metabolic dysregulation in HL-1 cells

Tumour necrosis factor (TNF)‐α induces cardiac metabolic disorder and mitochondrial dysfunction. Hydrogen sulphide (H₂S) contains anti‐inflammatory and biological effects in cardiomyocytes. This study investigated whether H₂S modulates TNF‐α‐dysregulated mitochondrial function and metabolism in cardiomyocytes. HL‐1 cells were incubated with TNF‐α (25 ng/mL) with or without sodium hydrosulphide (NaHS, 0.1 mmol/L) for 24 hours. Cardiac peroxisome proliferator‐activated receptor (PPAR) isoforms, pro‐inflammatory cytokines, receptor for advanced glycation end products (RAGE) and fatty acid metabolism were evaluated through Western blotting. The mitochondrial oxygen consumption rate and adenosine triphosphate (ATP) production were investigated using Seahorse XF24 extracellular flux analyzer and bioluminescence assay. Fluorescence intensity using 2′, 7′‐dichlorodihydrofluorescein diacetate was used to evaluate mitochondrial oxidative stress. NaHS attenuated the impaired basal and maximal respiration, ATP production and ATP synthesis and enhanced mitochondrial oxidative stress in TNF‐α‐treated HL‐1 cells. TNF‐α‐treated HL‐1 cells exhibited lower expression of PPAR‐α, PPAR‐δ, phosphorylated 5′ adenosine monophosphate‐activated protein kinase‐α2, phosphorylated acetyl CoA carboxylase, carnitine palmitoyltransferase‐1, PPAR‐γ coactivator 1‐α and diacylglycerol acyltransferase 1 protein, but higher expression of PPAR‐γ, interleukin‐6 and RAGE protein than control or combined NaHS and TNF‐α‐treated HL‐1 cells. NaHS modulates the effects of TNF‐α on mitochondria and the cardiometabolic system, suggesting its therapeutic potential for inflammation‐induced cardiac dysfunction.

Hydrogen sulfide protects against DSS-induced colitis by inhibiting NLRP3 inflammasome

Hydrogen sulfide (H₂S), as the third gasotransmitter, has been shown to be effective in the prevention of inflammation. In addition, the NLRP3 inflammasome is a key player in the pathogenesis of dextran sulfate sodium (DSS)-induced colitis. Therefore, the aim of our research was to determine whether H₂S exerts an anti-inflammatory effect on DSS-induced colitis by targeting NLRP3 inflammasome. Our data showed that DSS-induced colitis is attenuated by H₂S, lessening the shortening of the colon lengths and colonic pathological damages. The cytokines TNF-α, IL-1β, and IL-6 in colon samples were also significantly downregulated by H₂S. Besides, H₂S markedly suppressed the expression of NLRP3 and cleaved caspase-1 (p20) in colons from DSS-induced colitis mice. More importantly, CSE^-/- mice were more susceptive to DSS-induced colitis when compared to wild-type (WT) mice. Our experimental results also suggested that H₂S dose-dependently inhibits the activation of NLRP3 inflammasome in bone marrow-derived macrophages (BMDMs) by reducing the cleavage of caspase-1 and the secretion of IL-1β. Furthermore, the inhibitory effect of H₂S is due to a reduction in reactive oxygen species (ROS) generation and partly dependent on the disruption of nuclear erythroid 2-related factor-2 (Nrf2) activation. Collectively, our study confirms that H₂S exerts its protective effect on DSS-induced mouse colitis at least partly by inhibiting the activation of NLRP3 inflammasome pathway.

Association study of the CTH 1364 G>T polymorphism with coronary artery disease in the Greek population

Background Cystathionine γ-lyase enzyme, which is encoded by the CTH gene, is responsible for hydrogen sulfide (H2S) production in the endothelium. The CTH 1364 G>T polymorphism may alter the CTH expression and H2S bioavailability, thus leading to atherosclerosis and coronary artery disease (CAD). We examined the potential association of the CTH 1364 G>T polymorphism with CAD. Methods The CTH 1364 G>T polymorphism was determined in 178 coronary artery bypass grafting (CABG) patients and 156 non-atherosclerotic controls of Greek Caucasian origin using the PCR-RFLP method. Results No significant difference in the frequency of the CTH 1364 G>T genotypes (p = 0.281) and alleles (p = 0.265) was found between the CABG patients and controls. After conducting stratification according to sex, analysis showed a numerical difference in the CTH 1364 TT genotype frequency in female participants that did not reach statistical significance (16.3% and 8.5% in the CABG and controls, respectively, p = 0.26). The frequency of the CTH 1364 TT genotype between the male CABG patients and controls did not differ (p = 0.507). Conclusions The CTH 1364 G>T polymorphism was not associated with CAD in the studied population. However, interestingly, a higher - if not significantly so - CTH 1364 TT genotype frequency was present in female CABG patients compared with female controls. Larger studies are necessary to conclude on the potential overall or gender-driven association between CTH 1364 G>T gene polymorphism and CAD.

Metabolism of sulfur compounds in homocystinurias

BACKGROUND AND PURPOSE

Homocystinurias are rare genetic defects characterized by altered fluxes of sulfur compounds including homocysteine and cysteine. We explored whether the severely perturbed sulfur amino acid metabolism in patients with homocystinurias affects the metabolism of hydrogen sulfide.

EXPERIMENTAL APPROACH

We studied 10 treated patients with a block in the conversion of homocysteine to cysteine due to cystathionine β-synthase deficiency (CBSD) and six treated patients with remethylation defects (RMD) and an enhanced flux of sulfur metabolites via transsulfuration. Control groups for CBSD and RMD patients consisted of 22 patients with phenylketonuria on a low-protein diet and of 12 healthy controls respectively. Plasma and urine concentrations of selected sulfur compounds were analysed by HPLC and LC-MS/MS.

KEY RESULTS

Patients with CBSD exhibited plasma concentrations of monobromobimane-detected sulfide similar to appropriate controls. Urinary homolanthionine and thiosulfate in CBSD were increased significantly 1.9 and 3 times suggesting higher hydrogen sulfide synthesis by γ-cystathionase and detoxification respectively. Surprisingly, patients with RMD had significantly lower plasma sulfide levels (53 and 64% of controls) with lower sulfite concentrations, and higher taurine and thiosulfate levels suggesting enhanced cysteine oxidation and hydrogen sulfide catabolism respectively.

CONCLUSION AND IMPLICATIONS

The results from this study suggest that severe inherited defects in sulfur amino acid metabolism may be accompanied by only moderately perturbed hydrogen sulfide metabolism and lends support to the hypothesis that enzymes in the transsulfuration pathway may not be the major contributors to the endogenous hydrogen sulfide pool.

LINKED ARTICLES

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

Clopidogrel as a donor probe and thioenol derivatives as flexible promoieties for enabling H2S biomedicine

Hydrogen sulfide has emerged as a critical endogenous signaling transmitter and a potentially versatile therapeutic agent. The key challenges in this field include the lack of approved hydrogen sulfide-releasing probes for in human exploration and the lack of controllable hydrogen sulfide promoieties that can be flexibly installed for therapeutics development. Here we report the identification of the widely used antithrombotic drug clopidogrel as a clinical hydrogen sulfide donor. Clopidogrel is metabolized in patients to form a circulating metabolite that contains a thioenol substructure, which is found to undergo spontaneous degradation to release hydrogen sulfide. Model studies demonstrate that thioenol derivatives are a class of controllable promoieties that can be conveniently installed on a minimal structure of ketone with an α-hydrogen. These results can provide chemical tools for advancing hydrogen sulfide biomedical research as well as developing hydrogen sulfide-releasing drugs.

Hydrogen sulphide (H₂S) is a gaseous signalling molecule, which has shown therapeutic value. Here, the authors show that a thioenol metabolite of the antithrombotic drug clopidogrel is an efficient H₂S donor and masked thioenols can be linked to existing compounds to develop H₂S-releasing agents.

The effect of hydroalcoholic extract of Teucrium polium L. on the inflammatory markers and lipid profile in hypercholesterolemic rats

Background

Cardiovascular diseases are among the most common causes of mortality worldwide. Therefore, it is necessary to control the risk factors of these patients. Since the level of inflammatory markers and lipid profiles has increased in cardiovascular diseases and due to the increasing role of plants in the treatment of diseases, the current study aimed to investigate the effect of hydroalcoholic extract of Teucrium polium on inflammatory markers and lipid profile in hypercholesterolemic rats.

Materials and methods

A total of 24 adult male Wistar rats were randomly divided into four groups of six each and treated with oral administration for 8 weeks. The control group received normal diet, the sham group received high-cholesterol diet and experimental groups 1 and 2 received high-cholesterol diet in the 8 weeks and doses of 85 and 170 mg/kg, respectively, of the T. polium hydroalcoholic extract (TPHAE) in the second 4 weeks. At the beginning and the end of the study, rats were examined for biochemical parameters. The mean level of variables for each group was presented as mean ± standard error of mean.

Results

The results of this study showed that, after administration of TPHAE, there was a significant decrease in the mean of inflammatory markers in all groups compared to sham group (P<0.001). Also, administration of the extract significantly reduced the serum levels of triglyceride, cholesterol and LDL-cholesterol and significantly increased the serum HDL-cholesterol levels. In addition, the 170 mg/kg dose of TPHAE was the most effective in reducing serum levels of inflammatory and lipid markers.

Conclusion

Treatment with TPHAE caused dose-dependent decrease in serum levels of inflammatory markers and lipid profile in hypercholesterolemic rats. Therefore, it can be applied as a natural product for the management of cardiovascular diseases.

Evaluating Causality of Gut Microbiota in Obesity and Diabetes in Humans

The pathophysiology of obesity and obesity-related diseases such as type 2 diabetes mellitus (T2DM) is complex and driven by many factors. One of the most recently identified factors in development of these metabolic pathologies is the gut microbiota. The introduction of affordable, high-throughput sequencing technologies has substantially expanded our understanding of the role of the gut microbiome in modulation of host metabolism and (cardio)metabolic disease development. Nevertheless, evidence for a role of the gut microbiome as a causal, driving factor in disease development mainly originates from studies in mouse models: data showing causality in humans are scarce. In this review, we will discuss the quality of evidence supporting a causal role for the gut microbiome in the development of obesity and diabetes, in particular T2DM, in humans. Considering overlap in potential mechanisms, the role of the gut microbiome in type 1 diabetes mellitus will also be addressed. We will elaborate on factors that drive microbiome composition in humans and discuss how alterations in microbial composition or microbial metabolite production contribute to disease development. Challenging aspects in determining causality in humans will be postulated together with strategies that might hold potential to overcome these challenges. Furthermore, we will discuss means to modify gut microbiome composition in humans to help establish causality and discuss systems biology approaches that might hold the key to unravelling the role of the gut microbiome in obesity and T2DM.

(-)-Epigallocatechin-3-Gallate Ameliorates Atherosclerosis and Modulates Hepatic Lipid Metabolic Gene Expression in Apolipoprotein E Knockout Mice: Involvement of TTC39B

Background: Aberrant chronic inflammation and excess accumulation of lipids play a pivotal role in the occurrence and progression of atherosclerosis. (–)-Epigallocatechin-3-gallate (EGCG), the major catechins in green tea, displayed anti-atherosclerotic properties in vivo and in vitro. However, the effects and underlying mechanism of EGCG on atherosclerosis remain unclear.

Methods: Male apolipoprotein E-knockout (ApoE^-/-) mice (7 weeks old) fed with high-fat diet (HFD) were treated with normal saline or EGCG (40 mg/kg/d, i.g.) for 18 weeks. Atherosclerotic plaque and liver lipid accumulation were measured by Oil Red staining. Plasma lipids and cytokines were detected using commercial kits. The expression of protein and mRNA was analyzed by western blot and quantitative real-time reverse transcription-polymerase chain reaction, respectively.

Results: EGCG administration markedly attenuated atherosclerotic plaque formation in HFD-fed ApoE^-/- mice, which were accompanied by increased plasma interleukin-10 (IL-10) level and decreased plasma IL-6 and tumor necrosis factor-α (TNF-α) levels. In addition, EGCG modulated high-fat-induced dyslipidemia, evidencing by decreased total cholesterol (TC) and low-density lipoprotein levels and increased high-density lipoprotein level. Meanwhile, EGCG treatment alleviated high-fat-mediated liver lipid accumulation and decreased liver TC and triglyceride. Mechanistically, EGCG significantly modulated high-fat-induced hepatic tetratricopeptide repeat domain protein 39B (TTC39B) expression and its related genes (Lxrβ, Abcg5, Abcg8, Abca1, Srebf1, Scd1, Scd2, Fas, Elovl5, Mylip) expression in liver from ApoE^-/- mice. Notably, EGCG remarkably induced hepatic liver X receptor α (LXRα) and LXRβ expression and inhibited both precursor and mature sterol regulatory element binding transcription factor-1 (SREBP-1) expression.

Conclusion: Taken together, our data for the first time suggested that TTC39B was involved in EGCG-mediated anti-atherosclerotic effects through modulation of LXR/SREBP-1 pathway.