Effects of hydrogen sulfide on hypoxic pulmonary vascular structural remodeling

Hydrogen Sulfide Biomedical Research in China-20 Years of Hindsight

Hydrogen sulfide (H2S) is an important gasotransmitter that is produced by mammalian cells and performs profound physiological and pathophysiological functions. Biomedical research on H2S metabolism and function in China began 20 years ago, which pioneered the examination of the correlation of abnormal H2S metabolism and cardiovascular diseases. Over the last two decades, research teams in China have made numerous breakthrough discoveries on the effects of H2S metabolism on hypertension, atherosclerosis, pulmonary hypertension, shock, angiogenesis, chronic obstructive pulmonary disease, pain, iron homeostasis, and testicle function, to name a few. These research developments, carried by numerous research teams all over China, build nationwide research network and advance both laboratory study and clinical applications. An integrated and collaborative research strategy would further promote and sustain H2S biomedical research in China and in the world.

Implications of Hydrogen Sulfide in Development of Pulmonary Hypertension

The pathological mechanisms underlying pulmonary hypertension (PH), as well as its treatment strategy, are crucial issues in this field. This review aimed to summarize the pathological mechanisms by which the hydrogen sulfide (H2S) pathway contributes to PH development and its future implications. The data in this review were obtained from Medline and PubMed sources up to 2022 using the search terms "hydrogen sulfide" and "pulmonary hypertension". In the review, we discussed the significance of endogenous H2S pathway alteration in PH development and showed the advance of the role of H2S as the third gasotransmitter in the mechanisms for hypoxic PH, monocrotaline-induced PH, high blood flow-induced PH, and congenital heart disease-associated PH. Notably, H2S plays a crucial role in the development of PH via certain mechanisms, such as inhibiting the proliferation of pulmonary artery smooth muscle cells, suppressing the inflammation and oxidative stress of pulmonary artery endothelial cells, inducing pulmonary artery smooth muscle cell apoptosis, and interacting with other gaseous signaling pathways. Recently, a variety of H2S donors were developed, including naturally occurring donors and synthetic H2S donors. Therefore, understanding the role of H2S in PH development may help in further exploring novel potential therapeutic targets of PH.

H2S signaling and extracellular matrix remodeling in cardiovascular diseases: A tale of tense relationship

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network that not only provides mechanical support but also transduces essential molecular signals in organ functions. ECM is constantly remodeled to control tissue homeostasis, responsible for cell adhesion, cell migration, cell-to-cell communication, and cell differentiation, etc. The dysregulation of ECM components contributes to various diseases, including cardiovascular diseases, fibrosis, cancer, and neurodegenerative diseases, etc. Aberrant ECM remodeling is initiated by various stress, such as oxidative stress, inflammation, ischemia, and mechanical stress, etc. Hydrogen sulfide (H₂S) is a gasotransmitter that exhibits a wide variety of cytoprotective and physiological functions through its anti-oxidative and anti-inflammatory actions. Amounting research shows that H₂S can attenuate aberrant ECM remodeling. In this review, we discussed the implications and mechanisms of H₂S in the regulation of ECM remodeling in cardiovascular diseases, and highlighted the potential of H₂S in the prevention and treatment of cardiovascular diseases through attenuating adverse ECM remodeling.

Gasping for Sulfide: A Critical Appraisal of Hydrogen Sulfide in Lung Disease and Accelerated Aging

Hydrogen sulfide (H₂S) is a gaseous signaling molecule involved in a plethora of physiological and pathological processes. It is primarily synthesized by cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase as a metabolite of the transsulfuration pathway. H₂S has been shown to exert beneficial roles in lung disease acting as an anti-inflammatory and antiviral and to ameliorate cell metabolism and protect from oxidative stress. H₂S interacts with transcription factors, ion channels, and a multitude of proteins via post-translational modifications through S-persulfidation ("sulfhydration"). Perturbation of endogenous H₂S synthesis and/or levels have been implicated in the development of accelerated lung aging and diseases, including asthma, chronic obstructive pulmonary disease, and fibrosis. Furthermore, evidence indicates that persulfidation is decreased with aging. Here, we review the use of H₂S as a biomarker of lung pathologies and discuss the potential of using H₂S-generating molecules and synthesis inhibitors to treat respiratory diseases. Furthermore, we provide a critical appraisal of methods of detection used to quantify H₂S concentration in biological samples and discuss the challenges of characterizing physiological and pathological levels. Considerations and caveats of using H₂S delivery molecules, the choice of generating molecules, and concentrations are also reviewed. Antioxid. Redox Signal. 35, 551-579.

Relationship Between Endogenous Hydrogen Sulfide and Pulmonary Vascular Indexes on High-Resolution Computed Tomography in Patients with Chronic Obstructive Pulmonary Disease

Objective

To explore the relationship between endogenous hydrogen sulfide (H₂S) and high-resolution computed tomography (HRCT) indexes in pulmonary vascular remodeling.

Methods

A total of 94 stable chronic obstructive pulmonary disease (COPD) patients were recruited for the study．Plasma H₂S levels were measured using fluorescence probe. Fluorescence quantitative polymerase chain reaction was used to measure H₂S synthase cystathionine-γ-lyase (CSE) mRNA and cystathionine-β-synthesis enzyme (CBS) mRNA. The main pulmonary artery diameter (mPAD), axial diagonal mPAD, coronal mPAD, sagittal mPAD, right pulmonary artery diameter (RPAD), left pulmonary artery diameter (LPAD), and ascending aortic diameter (AAD) and the percentage of total cross-sectional area of vessels less than 5 mm² of total lung area (%CSA <5) on HRCT were measured. Pulmonary arterial systolic pressure (PASP) of echocardiography, blood gas analysis, and routine blood tests were performed. Correlation analysis and multivariate linear regression were performed using SPSS 22.0.

Results

H₂S was negatively correlated with mPAD, axial diagonal mPAD, and sagittal mPAD (r = -0.25~-0.32) and positively correlated with PaO₂ (r = 0.35). Relative expression of CSE mRNA was positively correlated with PASP, coronal mPAD, sagittal mPAD, white blood cell count (WBC), and neutrophil count (N) (r = 0.30~0.44). The relative expression of CBS mRNA was positively correlated with PASP, WBC, and N (r = 0.34~0.41). In separate models predicting pulmonary vascular indexes, a 1μmol/L increase in H₂S predicted lower pulmonary artery diameter (for axial diagonal mPAD, 0.76mm lower; for mPAD/AAD, 0.68mm lower). All P values were less than 0.05.

Conclusion

Endogenous H₂S may be involved in pulmonary vascular remodeling, providing a new method for the diagnosis and treatment of COPD. The generation of H₂S may be inhibited by hypoxia, inflammation, etc.

An evolutionary perspective on the interplays between hydrogen sulfide and oxygen in cellular functions

The physiological effects of the endogenously generated hydrogen sulfide (H2S) have been extensively studied in recent years. This review summarized the role of H2S in the origin of life and H2S metabolism in organisms from bacteria to vertebrates, examined the relationship between H2S and oxygen from an evolutionary perspective and emphasized the oxygen-dependent manner of H2S signaling in various physiological and pathological processes. H2S and oxygen are inextricably linked in various cellular functions. H2S is involved in aerobic respiration and stimulates oxidative phosphorylation and ATP production within the cell. Besides, H2S has protective effects on ischemia and reperfusion injury in several organs by acting as an oxygen sensor. Also, emerging evidence suggests the role of H2S is in an oxygen-dependent manner. All these findings indicate the subtle relationship between H2S and oxygen and further explain why H2S, a toxic molecule thriving in an anoxia environment several billion years ago, still affects homeostasis today despite the very low content in the body.

Hydrogen Sulfide Metabolism and Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe and multifactorial disease characterized by a progressive elevation of pulmonary arterial resistance and pressure due to remodeling, inflammation, oxidative stress, and vasoreactive alterations of pulmonary arteries (PAs). Currently, the etiology of these pathological features is not clearly understood and, therefore, no curative treatment is available. Since the 1990s, hydrogen sulfide (H₂S) has been described as the third gasotransmitter with plethoric regulatory functions in cardiovascular tissues, especially in pulmonary circulation. Alteration in H₂S biogenesis has been associated with the hallmarks of PH. H₂S is also involved in pulmonary vascular cell homeostasis via the regulation of hypoxia response and mitochondrial bioenergetics, which are critical phenomena affected during the development of PH. In addition, H₂S modulates ATP-sensitive K⁺ channel (K_ATP) activity, and is associated with PA relaxation. In vitro or in vivo H₂S supplementation exerts antioxidative and anti-inflammatory properties, and reduces PA remodeling. Altogether, current findings suggest that H₂S promotes protective effects against PH, and could be a relevant target for a new therapeutic strategy, using attractive H₂S-releasing molecules. Thus, the present review discusses the involvement and dysregulation of H₂S metabolism in pulmonary circulation pathophysiology.

Modulation of EndMT by Hydrogen Sulfide in the Prevention of Cardiovascular Fibrosis

Endothelial mesenchymal transition (EndMT) has been described as a fundamental process during embryogenesis; however, it can occur also in adult age, underlying pathological events, including fibrosis. Indeed, during EndMT, the endothelial cells lose their specific markers, such as vascular endothelial cadherin (VE-cadherin), and acquire a mesenchymal phenotype, expressing specific products, such as α-smooth muscle actin (α-SMA) and type I collagen; moreover, the integrity of the endothelium is disrupted, and cells show a migratory, invasive and proliferative phenotype. Several stimuli can trigger this transition, but transforming growth factor (TGF-β1) is considered the most relevant. EndMT can proceed in a canonical smad-dependent or non-canonical smad-independent manner and ultimately regulate gene expression of pro-fibrotic machinery. These events lead to endothelial dysfunction and atherosclerosis at the vascular level as well as myocardial hypertrophy and fibrosis. Indeed, EndMT is the mechanism which promotes the progression of cardiovascular disorders following hypertension, diabetes, heart failure and also ageing. In this scenario, hydrogen sulfide (H₂S) has been widely described for its preventive properties, but its role in EndMT is poorly investigated. This review is focused on the evaluation of the putative role of H₂S in the EndMT process.

Understanding hydrogen sulfide signaling in neonatal airway disease

INTRODUCTION

Airway dysfunction leading to chronic lung disease is a common consequence of premature birth and mechanisms responsible for early and progressive airway remodeling are not completely understood. Current therapeutic options are only partially effective in reducing the burden of neonatal airway disease and premature decline of lung function. Gasotransmitter hydrogen sulfide (H2S) has been recently recognized for its therapeutic potential in lung diseases.

AREAS COVERED

Contradictory to its well-known toxicity at high concentrations, H2S has been characterized to have anti-inflammatory, antioxidant, and antiapoptotic properties at physiological concentrations. In the respiratory system, endogenous H2S production participates in late lung development and exogenous H2S administration has a protective role in a variety of diseases such as acute lung injury and chronic pulmonary hypertension and fibrosis. Literature searches performed using NCBI PubMed without publication date limitations were used to construct this review, which highlights the dichotomous role of H2S in the lung, and explores its promising beneficial effects in lung diseases.

EXPERT OPINION

The emerging role of H2S in pathways involved in chronic lung disease of prematurity along with its recent use in animal models of BPD highlight H2S as a potential novel candidate in protecting lung function following preterm birth.

Hydrogen sulfide and vascular regulation - An update

BACKGROUND

Hydrogen sulfide (H₂S) is considered to be the third gasotransmitter after carbon monoxide (CO) and nitric oxide (NO). It plays an important role in the regulation of vascular homeostasis. Vascular remodeling have has proved to be related to the impaired H₂S generation.

AIM OF REVIEW

This study aimed to summarize and discuss current data about the function of H₂S in vascular physiology and pathophysiology as well as the underlying mechanisms.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Endogenous hydrogen sulfide (H₂S) as a third gasotransmitter is primarily generated by the enzymatic pathways and regulated by several metabolic pathways. H₂S as a physiologic vascular regulator, inhibits proliferation, regulates its apoptosis and autophagy of vascular cells and controls the vascular tone. Accumulating evidence shows that the downregulation of H₂S pathway is involved in the pathogenesis of a variety of vascular diseases, such as hypertension, atherosclerosis and pulmonary hypertension. Alternatively, H₂S supplementation may greatly help to prevent the progression of the vascular diseases by regulating vascular tone, inhibiting vascular inflammation, protecting against oxidative stress and proliferation, and modulating vascular cell apoptosis, which has been verified in animal and cell experiments and even in the clinical investigation. Besides, H₂S system and angiotensin-converting enzyme (ACE) inhibitors play a vital role in alleviating ischemic heart disease and left ventricular dysfunction. Notably, sulfhydryl-containing ACEI inhibitor zofenopril is superior to other ACE inhibitors due to its capability of H₂S releasing, in addition to ACE inhibition. The design and application of novel H₂S donors have significant clinical implications in the treatment of vascular-related diseases. However, further research regarding the role of H₂S in vascular physiology and pathophysiology is required.

Protein biomarkers and risk scores in pulmonary arterial hypertension associated with ventricular septal defect: integration of multi-omics and validation

The molecular mechanisms underlying pulmonary arterial hypertension (PAH) in congenital ventricular septal defects (VSD) are unclear. We aimed to reveal molecular pathways and potential biomarkers by multi-omics analysis in VSD-PAH. Plasma from 160 children, including 120 VSD patients with/without PAH and 40 healthy children was studied by integrated proteomics, metabolomics, and bioinformatics analyses. Proteomics identified 107 differential proteins (DPs) between patients with/without PAH including significantly increased adiponectin (ADIPO), dopamine β-hydroxylase (DBH), alanyl membrane aminopeptidase (ANPEP), transferrin receptor 1, and glycoprotein Ib platelet α-subunit and decreased guanine nucleotide-binding protein Gs in VSD-PAH. Metabolomics discovered 191 differential metabolites between patients with/without PAH, including elevation of serotonin, taurine, creatine, sarcosine, and 2-oxobutanoate, and decrease of vanillylmandelic acid, 3,4-dihydroxymandelate, 15-keto-prostaglandin F_2α, fructose 6-phosphate, l-glutamine, dehydroascorbate, hydroxypyruvate, threonine, l-cystine, and 1-aminocyclopropane-1-carboxylate. The DPs were validated in a new cohort of patients (n = 80). Integrated analyses identified key pathways, including cAMP, ECM receptor interaction, AMPK, hypoxia-inducible factor 1, PI3K-Akt signaling pathways, and amino acid metabolisms. Increased plasma protein levels of DBH, ADIPO, and ANPEP were found to be independently associated with the occurrence of PAH, with a new total risk score from these three proteins developed for clinical diagnosis. In this integrated multi-omics analysis in VSD-PAH patients, we have, for the first time, found that VSD-PAH patients present important differential proteins, metabolites, and key pathways. We have developed a total risk score (based on the plasma concentration of DBH, ANPEP, and ADIPO) as a predictor of development of PAH in CHD-VSD patients. Therefore, these proteins may be used as biomarkers, and the new total risk score has significant clinical implications in the diagnosis of PAH.

A biotin-guided hydrogen sulfide fluorescent probe and its application in living cell imaging

Hydrogen sulfide (H2S), a well-known signaling molecule, exerts significant regulatory effects on the cardiovascular and nervous systems. Therefore, monitoring the metabolism of H2S offers a potential mechanism to detect various diseases. In addition, biotin is significantly used as a targeting group to detect cancer cells exclusively. In this work, a biotin-guided benzoxadizole-based fluorescent probe, NP-biotin, was developed for H2S detection and evaluated in normal liver cell (LO2) and liver cancer cell (HepG2) lines. Results reveal that NP-biotin can detect cellular H2S with high sensitivity and selectivity. Moreover, NP-biotin has been confirmed to possess the ability to target cancer cells under the guidance of the biotin group.

Reactive Oxygen Species-Dependent Calpain Activation Contributes to Airway and Pulmonary Vascular Remodeling in Chronic Obstructive Pulmonary Disease

Aims: Airway and pulmonary vascular remodeling is an important pathological feature in the pathogenesis of chronic obstructive pulmonary disease (COPD). Tobacco smoke (TS) induces the production of large amounts of reactive oxygen species (ROS) in COPD lungs. We investigated how ROS lead to airway and pulmonary vascular remodeling in COPD. Results: We used in vitro bronchial and pulmonary artery smooth muscle cells (BSMCs and PASMCs), in vivo TS-induced COPD rodent models, and lung tissues of COPD patients. We found that H2O2 and TS extract (TSE) induced calpain activation in BSMCs and PASMCs. Calpain activation was elevated in smooth muscle of bronchi and pulmonary arterioles in COPD patients and TS-induced COPD rodent models. Calpain inhibition attenuated H2O2- and TSE-induced collagen synthesis and proliferation of BSMCs and PASMCs. Exposure to TS causes increases in airway resistance, right ventricular systolic pressure (RVSP), and thickening of bronchi and pulmonary arteries. Calpain inhibition by smooth muscle-specific knockout of calpain and the calpain inhibitor MDL28170 attenuated increases in airway resistance, RVSP, and thickening of bronchi and pulmonary arteries. Moreover, smooth muscle-specific knockout of calpain did not reduce TS-induced emphysema in the mouse model, but MDL28170 did reduce TS-induced emphysema in the rat model. Innovation: This study provides the first evidence that ROS-induced calpain activation contributes to airway and pulmonary vascular remodeling in TS-induced COPD. Calpain might be a novel therapeutic target for the treatment of COPD. Conclusion: These results indicate that ROS-induced calpain activation contributes to airway and pulmonary vascular remodeling and pulmonary hypertension in COPD.

Protective effect of hydrogen sulfide on monocrotaline‑induced pulmonary arterial hypertension via inhibition of the endothelial mesenchymal transition

Endothelial‑to‑mesenchymal transition (EndMT) serves an important role in the vascular remodeling of pulmonary arterial hypertension (PAH). However, little is known about the correlation between hydrogen sulfide (H2S), a protective gaseous mediator in PAH and the process of EndMT. Male Sprague‑Dawley rats (10 weeks old) received a single dose of monocrotaline (MCT; i.p., 60 mg/kg) and were randomly treated with NaHS [an H2S donor; intraperitoneal (i.p.) 1 mg/kg/day], DL‑propagylglycine (an inhibitor of H2S synthesis; PAG; i.p., 10 mg/kg/day) or saline, 7 days after MCT injection. Rats were sacrificed 21 days after MCT injection. A selection of human pulmonary artery endothelial cells (HPAECs) were pretreated with NaHS or saline and stimulated with transforming growth factor (TGF)‑β1 (10 ng/ml), and the other HPAECs were transfected with a cystathionine γ‑lyase (CSE, an H2S synthesizing enzyme) plasmid and subsequently stimulated with TGF‑β1. NaHS was indicated to inhibit EndMT and PAH progression by inhibiting the induction of the nuclear factor (NF)‑κB‑Snail pathway. In contrast, the depletion of H2S formation by PAG exacerbated EndMT and PAH by activating NF‑κB‑Snail molecules. In HPAECs, NaHS dose‑dependently inhibited TGF‑β1‑induced EndMT and the activation of the NF‑κB‑Snail pathway. Transfection with a CSE plasmid significantly repressed TGF‑β1‑induced expression of the mesenchymal marker and upregulated the expression of the endothelial marker, which was accompanied by the suppression of the NF‑κB‑Snail pathway. The inhibitory effect of CSE overexpression on TGF‑β1‑induced EndMT was significantly reversed by pretreatment with PAG. In conclusion, the current study provides novel information elucidating the beneficial effect of H2S on PAH through inhibiting the induction of the NF‑κB‑Snail pathway and the subsequent process of EndMT in pulmonary arteries.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

Hydrogen sulfide in physiology and pathogenesis of bacteria and viruses

An increasing number of studies have established hydrogen sulfide (H₂S) gas as a major cytoprotectant and redox modulator. Following its discovery, H₂S has been found to have pleiotropic effects on physiology and human health. H₂S acts as a gasotransmitter and exerts its influence on gastrointestinal, neuronal, cardiovascular, respiratory, renal, and hepatic systems. Recent discoveries have clearly indicated the importance of H₂S in regulating vasorelaxation, angiogenesis, apoptosis, ageing, and metabolism. Contrary to studies in higher organisms, the role of H₂S in the pathophysiology of infectious agents such as bacteria and viruses has been less studied. Bacterial and viral infections are often accompanied by changes in the redox physiology of both the host and the pathogen. Emerging studies indicate that bacterial-derived H₂S constitutes a defense system against antibiotics and oxidative stress. The H₂S signaling pathway also seems to interfere with redox-based events affected on infection with viruses. This review aims to summarize recent advances on the emerging role of H₂S gas in the bacterial physiology and viral infections. Such studies have opened up new research avenues exploiting H₂S as a potential therapeutic intervention.

Lack of association between urotensin-II (UTS2) gene polymorphisms (Thr21Met and Ser89Asn) and migraine

Migraine is a common neurovascular brain disorder with heterogeneous clinical presentation, including recurrent headache attacks. The pathophysiology of migraine is complex, and a number of genomic regions have been associated with the development of migraine. In this study, we analyzed the allele and genotype frequencies of the urotensin-II gene (UTS2) polymorphisms, Thr21Met and Ser89Asn, among Turkish patients with migraine. A total of 146 patients with migraine (14 with aura [MA group] and 132 without aura [MO group]) were genotyped for Thr21Met and Ser89Asn polymorphisms and compared with 154 age- and sex-matched healthy controls. The UTS2 gene polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). No significant differences were observed in allele and genotype frequencies for Thr21Met and Ser89Asn polymorphisms between the patients with migraine and control group. Similarly, we did not observe significant differences in allele and genotype frequencies between MA and MO and control group. Moreover, the haplotype analysis showed no association between UTS2 gene haplotypes (MN, MS, TN, and TS) and migraine. In summary, Thr21Met and Ser89Asn polymorphisms of the UTS2 gene are not risk factors for migraine in our sample of Turkish migraine patients.

Endogenous Hydrogen Sulfide Enhances Carotid Sinus Baroreceptor Sensitivity by Activating the Transient Receptor Potential Cation Channel Subfamily V Member 1 (TRPV1) Channel

Background

We aimed to investigate the regulatory effects of hydrogen sulfide (H₂S) on carotid sinus baroreceptor sensitivity and its mechanisms.

Methods and Results

Male Wistar‐Kyoto rats and spontaneously hypertensive rats (SHRs) were used in the experiment and were given an H₂S donor or a cystathionine‐β‐synthase inhibitor, hydroxylamine, for 8 weeks. Systolic blood pressure and the cystathionine‐β‐synthase/H₂S pathway in carotid sinus were detected. Carotid sinus baroreceptor sensitivity and the functional curve of the carotid baroreceptor were analyzed using the isolated carotid sinus perfusion technique. Effects of H₂S on transient receptor potential cation channel subfamily V member 1 (TRPV1) expression and S‐sulfhydration were detected. In SHRs, systolic blood pressure was markedly increased, but the cystathionine‐β‐synthase/H₂S pathway in the carotid sinus was downregulated in comparison to that of Wistar‐Kyoto rats. Carotid sinus baroreceptor sensitivity in SHRs was reduced, demonstrated by the right and upward shift of the functional curve of the carotid baroreceptor. Meanwhile, the downregulation of TRPV1 protein was demonstrated in the carotid sinus; however, H₂S reduced systolic blood pressure but enhanced carotid sinus baroreceptor sensitivity in SHRs, along with TRPV1 upregulation in the carotid sinus. In contrast, hydroxylamine significantly increased the systolic blood pressure of Wistar‐Kyoto rats, along with decreased carotid sinus baroreceptor sensitivity and reduced TRPV1 protein expression in the carotid sinus. Furthermore, H₂S‐induced enhancement of carotid sinus baroreceptor sensitivity of SHRs could be amplified by capsaicin but reduced by capsazepine. Moreover, H₂S facilitated S‐sulfhydration of TRPV1 protein in the carotid sinus of SHRs and Wistar‐Kyoto rats.

Conclusions

H₂S regulated blood pressure via an increase in TRPV1 protein expression and its activity to enhance carotid sinus baroreceptor sensitivity.

Placental Stem Villus Arterial Remodeling Associated with Reduced Hydrogen Sulfide Synthesis Contributes to Human Fetal Growth Restriction

Intrauterine fetal growth restriction (IUGR) is often associated with compromised umbilical arterial flow, indicating increased placental vascular resistance. Oxidative stress is causatively implicated. Hydrogen sulfide maintains differentiated smooth muscle in vascular beds, and its synthetic enzyme cystathionine-γ-lyase (CSE) is down-regulated in growth-restricted placentas. We hypothesized that remodeling of resistance arteries in stem villi contributes to IUGR by compromising umbilical blood flow via oxidative stress, reducing hydrogen sulfide signaling. Stem villus arteries in human IUGR placentas displaying absent or reversed end-diastolic flow contained reduced myosin heavy chain, smooth muscle actin, and desmin, and increased markers of dedifferentiation, cellular retinol-binding protein 1, and matrix metalloproteinase 2, compared to term and preterm controls. Wall thickness/lumen ratio was increased, lumen diameter decreased, but wall thickness remained unchanged in IUGR placentas. CSE correlated positively with myosin heavy chain, smooth muscle actin, and desmin. Birth weight correlated positively with CSE, myosin heavy chain, smooth muscle actin, and desmin, and negatively with cellular retinol-binding protein 1 and matrix metalloproteinase 2. These findings could be recapitulated in vitro by subjecting stem villus artery explants to hypoxia-reoxygenation, or inhibiting CSE. Treatment with a hydrogen sulfide donor, diallyl trisulfide, prevented these changes. IUGR is associated with vascular remodeling of the stem villus arteries. Oxidative stress results in reduction of placental CSE activity, decreased hydrogen sulfide production, and smooth muscle cell dedifferentiation in vitro. This vascular remodeling is reversible, and hydrogen sulfide donors are likely to improve pregnancy outcomes.

Hydrogen sulfide depletion contributes to microvascular remodeling in obesity

Structural remodeling of the microvasculature occurs during obesity. Based on observations that impaired H2S signaling is associated with cardiovascular pathologies, the current study was designed to test the hypothesis that altered H2S homeostasis is involved in driving the remodeling process in a diet-induced mouse model of obesity. The structural and passive mechanical properties of mesenteric resistance arterioles isolated from 30-wk-old lean and obese mice were assessed using pressure myography, and vessel H2S levels were quantified using the H2S indicator sulfidefluor 7-AM. Remodeling gene expression was assessed using quantitative RT-PCR, and histological staining was used to quantify vessel collagen and elastin. Obesity was found to be associated with decreased vessel H2S concentration, inward hypertrophic remodeling, altered collagen-to-elastin ratio, and reduced vessel stiffness. In addition, mRNA levels of fibronectin, collagen types I and III, matrix metalloproteinases 2 and 9, and tissue inhibitor of metalloproteinase 1 were increased and elastin was decreased by obesity. Evidence that decreased H2S was responsible for the genetic changes was provided by experiments in which H2S levels were manipulated, either by inhibition of the H2S-generating enzyme cystathionine γ-lyase with dl-propargylglycine or by incubation with the H2S donor GYY4137. These data suggest that, during obesity, depletion of H2S is involved in orchestrating the genetic changes underpinning inward hypertrophic remodeling in the microvasculature.

The vasodilatory effect of sulfur dioxide via SGC/cGMP/PKG pathway in association with sulfhydryl-dependent dimerization

The present study was designed to explore the role of soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/PKG pathway in sulfur dioxide (SO2)-induced vasodilation. We showed that SO2 induced a concentration-dependent relaxation of phenylephrine (PE)-precontracted rat aortic rings in association with an increase in cGMP concentration, whereas l-aspartic acid β-hydroxamate (HDX), an inhibitor of SO2 synthase, contracted rings in a dose-dependent manner. Pretreatment of aortic rings with the sGC inhibitor ODQ (30 μM) attenuated the vasodilatory effects of SO2, suggesting the involvement of cGMP pathway in SO2-induced vasodilation. Mechanistically, SO2 upregulated the protein levels of sGC and PKG dimers, while HDX inhibited it, indicating SO2 could promote cGMP synthesis through sGC activation. Furthermore, the dimerization of sGC and PKG and vasodilation induced by SO2 in precontracted rings were significantly prevented by thiol reductants dithiothreitol (DTT). In addition, SO2 reduced the activity of phosphodiesterase type 5 (PDE5), a cGMP-specific hydrolytic enzyme, implying that SO2 elevated cGMP concentration by inhibiting its hydrolysis. Hence, SO2 exerted its vasodilatory effects at least partly by promoting disulfide-dependent dimerization of sGC and PKG, resulting in an activated sGC/cGMP/PKG pathway in blood vessels. These findings revealed a new mode of action and mechanisms by which SO2 regulated the vascular tone.

Plasma H2S predicts coronary artery lesions in children with Kawasaki disease

BACKGROUND

The aim of this study was to determine whether plasma hydrogen sulfide (H2S) is a biomarker for predicting coronary artery lesions (CAL) in children with Kawasaki disease (KD).

METHODS

A prospective study was conducted on 50 KD patients and 27 healthy children. Plasma H2 S was analyzed at the acute stage. Plasma H2S was detected using the sensitive electrode method, and receiver operating characteristic curve (ROC) analysis was carried out.

RESULTS

Plasma H2S in KD patients at the acute stage was significantly lower than that of controls. CAL patients had reduced plasma H2S at acute stage compared with the non-CAL patients. A plasma H2S cut-off of 31.2 µmol/L provided a sensitivity of 81% and a specificity of 62.5% for predicting coronary injuries in KD. Optimal specificity and sensitivity were obtained when using plasma H2S to predict CAL in KD children.

CONCLUSION

Plasma H2S level in the acute period is a potentially useful biomarker for predicting CAL in KD children.

Caffeic Acid Phenethyl Ester inhibit Hepatic Fibrosis by Nitric Oxide Synthase and Cystathionine Gamma-Lyase in Rats

Background

Our aim was to study the effect of caffeic acid phenethyl ester (CAPE) on iNOS and cystathionine gamma-lyase (CSE) of hepatic fibrosis rat, and discuss the anti-hepatic fibrosis mechanism of caffeic acid phenethyl ester.

Material/Methods

We observed changes of NO and H₂S in serum of hepatic fibrosis rats. Enzyme-linked immunosorbent assay was used to test OD value of iNOS and CSE in serum of each. The expressions of iNOS and CSE protein in the liver were also detected by immunohistochemistry.

Results

Compared with the model group, the expression of NO and iNOS was decreased obviously and the level of H₂S and CSE was increased in the CAPE group.

Conclusions

CAPE has the effect of anti-hepatic fibrosis, which can be realized through adjusting the expression level of iNOS and CSE.

Matrix metalloproteinases in atherosclerosis: role of nitric oxide, hydrogen sulfide, homocysteine, and polymorphisms

Atherosclerosis is an inflammatory process that involves activation of matrix metalloproteinases (MMPs); MMPs degrade collagen and allow for smooth-muscle cell migration within a vessel. Moreover, this begets an accumulation of other cellular material, resulting in occlusion of the vessel and ischemic events to tissues in need of nutrients. Homocysteine has been shown to activate MMPs via an increase in oxidative stress and acting as a signaling molecule on receptors like the peroxisome proliferator activated receptor-γ and N-methyl-D-aspartate receptor. Nitric oxide has been shown to be beneficial in some cases of deactivating MMPs. However, in other cases, it has been shown to be harmful. Further studies are warranted on the scenarios that are beneficial versus destructive. Hydrogen sulfide (H₂S) has been shown to decrease MMP activities in all cases in the literature by acting as an antioxidant and vasodilator. Various MMP-knockout and gene-silencing models have been used to determine the function of the many different MMPs. This has allowed us to discern the role that each MMP has in promoting or alleviating pathological conditions. Furthermore, there has been some study into the MMP polymorphisms that exist in the population. The purpose of this review is to examine the role of MMPs and their polymorphisms on the development of atherosclerosis, with emphasis placed on pathways that involve nitric oxide, hydrogen sulfide, and homocysteine.

MMP-9- and NMDA receptor-mediated mechanism of diabetic renovascular remodeling and kidney dysfunction: hydrogen sulfide is a key modulator

Previously we reported that matrix metalloproteinase-9 (MMP-9) plays an important role in extracellular matrix (ECM) remodeling in diabetic kidney. Induction of NMDA-R and dysregulation of connexins (Cxs) were also observed. We concluded that this was due to decreased H2S production by downregulation of CBS and CSE enzymes. However, the potential role of H2S to mitigate ECM dysregulation and renal dysfunction was not clearly understood. The present study was undertaken to determine whether H2S supplementation reduces MMP-9-induced ECM remodeling and dysfunction in diabetic kidney. Wild type (C57BL/6J), diabetic (Akita, C57BL/6J-Ins2(Akita)), MMP-9 knockout (MMP-9(-/-), M9KO) and double KO of Akita/MMP-9(-/-) (DKO) mice were treated without or with 0.005 g/l of NaHS (as a source of H2S) in drinking water for 30 days. Decreased tissue production and plasma content of H2S in Akita mice were ameliorated with H2S supplementation. Dysregulated expression of MMP-9, CBS, CSE, NMDA-R1 and Cxs-40, -43 was also normalized in Akita mice treated with H2S. In addition, increased renovascular resistive index (RI), ECM deposition, plasma creatinine, and diminished renal vascular density and cortical blood flow in Akita mice were normalized with H2S treatment. We conclude that diminished H2S production in renal tissue and plasma levels in diabetes mediates adverse renal remodeling, and H2S therapy improves renal function through MMP-9- and NMDA-R1-mediated pathway.

Endogeous sulfur dioxide protects against oleic acid-induced acute lung injury in association with inhibition of oxidative stress in rats

The role of endogenous sulfur dioxide (SO2), an efficient gasotransmitter maintaining homeostasis, in the development of acute lung injury (ALI) remains unidentified. We aimed to investigate the role of endogenous SO2 in the pathogenesis of ALI. An oleic acid (OA)-induced ALI rat model was established. Endogenous SO2 levels, lung injury, oxidative stress markers and apoptosis were examined. OA-induced ALI rats showed a markedly downregulated endogenous SO2/aspartate aminotransferase 1 (AAT1)/AAT2 pathway and severe lung injury. Chemical colorimetry assays demonstrated upregulated reactive oxygen species generation and downregulated antioxidant capacity in OA-induced ALI rats. However, SO2 increased endogenous SO2 levels, protected against oxidative stress and alleviated ALI. Moreover, compared with OA-treated cells, in human alveolar epithelial cells SO2 downregulated O2(-) and OH(-) generation. In contrast, L-aspartic acid-β-hydroxamate (HDX, Sigma-Aldrich Corporation), an inhibitor of endogenous SO2 generating enzyme, promoted free radical generation, upregulated poly (ADP-ribose) polymerase expression, activated caspase-3, as well as promoted cell apoptosis. Importantly, apoptosis could be inhibited by the free radical scavengers glutathione (GSH) and N-acetyl-L-cysteine (NAC). The results suggest that SO2/AAT1/AAT2 pathway might protect against the development of OA-induced ALI by inhibiting oxidative stress.

Effect of hydrogen sulfide on inflammatory cytokines in acute myocardial ischemia injury in rats

Hydrogen sulfide (H₂S) is believed to be involved in numerous physiological and pathophysiological processes, and now it is recognized as the third endogenous signaling gasotransmitter, following nitric oxide and carbon monoxide; however, the effects of H₂S on inflammatory factors in acute myocardial ischemia injury in rats have not been clarified. In the present study, sodium hydrosulfide (NaHS) was used as the H₂S donor. Thirty-six male Sprague Dawley rats were randomly divided into five groups: Sham, ischemia, ischemia + low-dose (0.78 mg/kg) NaHS, ischemia + medium-dose (1.56 mg/kg) NaHS, ischemia + high-dose (3.12 mg/kg) NaHS and ischemia + propargylglycine (PPG) (30 mg/kg). The rats in each group were sacrificed 6 h after the surgery for sample collection. Compared with the ischemia group, the cardiac damage in the rats in the ischemia + NaHS groups was significantly reduced, particularly in the high-dose group; in the ischemia + PPG group, the myocardial injury was aggravated compared with that in the ischemia group. Compared with the ischemia group, the levels of interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α) in the serum of rats in the ischemia + medium- and high-dose NaHS groups were significantly reduced, and the expression of intercellular adhesion molecule-1 (ICAM-1) mRNA and nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) protein in the myocardial tissues of rats was significantly reduced. In the ischemia + PPG group, the TNF-α, IL-1β and IL-6 levels in the serum were significantly increased, the expression of ICAM-1 mRNA was increased, although without a significant difference, and the expression of NF-κB was increased. The findings of the present study provide novel evidence for the dual effects of H₂S on acute myocardial ischemia injury via the modulation of inflammatory factors.

CD47-dependent regulation of H₂S biosynthesis and signaling in T cells

Pharmacological concentrations of H2S donors inhibit some T cell functions by inhibiting mitochondrial function, but evidence is also emerging that H2S at physiological concentrations produced via chemical sources and endogenously is a positive physiological mediator of T cell function. Expression of the H2S biosynthetic enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) is induced in response to T cell receptor signaling. Inhibiting the induction of these enzymes limits T cell activation and proliferation, which can be overcome by exposure to exogenous H2S at submicromolar concentrations. Exogenous H2S at physiological concentrations increases the ability of T cells to form an immunological synapse by altering cytoskeletal actin dynamics and increasing the reorientation of the microtubule-organizing center. Downstream, H2S enhances T cell receptor-dependent induction of CD69, CD25, and Interleukin-2 (IL-2) gene expression. The T cell stimulatory activity of H2S is enhanced under hypoxic conditions that limit its oxidative metabolism by mitochondrial and nonenzymatic processes. Studies of the receptor CD47 have revealed the first endogenous inhibitory signaling pathway that regulates H2S signaling in T cells. Binding of the secreted protein thrombospondin-1 to CD47 elicits signals that block the stimulatory activity of exogenous H2S on T cell activation and limit the induction of CSE and CBS gene expression. CD47 signaling thereby inhibits T cell receptor-mediated T cell activation.

Modulation of hydrogen sulfide by vascular hypoxia

Hydrogen sulfide (H₂S) has emerged as a key regulator of cardiovascular function. This gasotransmitter is produced in the vasculature and is involved in numerous processes that promote vascular homeostasis, including vasodilation and endothelial cell proliferation. Although H₂S plays a role under physiological conditions, it has become clear in recent years that hypoxia modulates the production and action of H₂S. Furthermore, there is growing evidence that H₂S is cytoprotective in the face of hypoxic insults. This review focuses on the synthesis and signaling of H₂S in hypoxic conditions in the vasculature, and highlights recent studies providing evidence that H₂S is a potential therapy for preventing tissue damage in hypoxic conditions.

The therapeutic potential of antioxidants, ER chaperones, NO and H2S donors, and statins for treatment of preeclampsia

Preeclampsia is a complex multifactorial disease. Placental oxidative stress, a result of deficient spiral artery remodeling, plays an important role in the pathophysiology of preeclampsia. Antiangiogenic factors secreted from malperfused placenta are instrumental in mediating maternal endothelial dysfunction and consequent symptoms of preeclampsia; the mechanism is likely to involve increased ET-1 secretion and reduced NO bioavailability. Therapeutic interventions so far remain only experimental and there is no established remedy for the treatment of preeclampsia. This review concentrates on the evidence for the therapeutic potential of antioxidants, ER chaperones, NO and H2S donors, and statins. These compounds display pleitropic antioxidant, anti-inflammatory, and pro-angiogenic effects in animal and in vitro studies. Although clinical trials on the use of antioxidant vitamins in pregnancy proved largely unsuccessful, the scope for their use still exists given the beneficial cardioprotective effects of antioxidant-rich Mediterranean diet, periconceptual vitamin use and the synergistic effect of vitamin C and L-arginine. Encouraging clinical evidence exists for the use of NO donors, and a clinical trial is underway testing the effect of statins in treatment of preeclampsia. H2S recently emerged as a novel therapeutic agent for cardiovascular disease, and its beneficial effects were also tested in animal models of preeclampsia. It is risky to prescribe any medication to pregnant women on a large scale, and any future therapeutic intervention has to be well tested and safe. Many of the compounds discussed could be potential candidates.

Antenatal hypoxia and pulmonary vascular function and remodeling

This review provides evidence that antenatal hypoxia, which represents a significant and worldwide problem, causes prenatal programming of the lung. A general overview of lung development is provided along with some background regarding transcriptional and signaling systems of the lung. The review illustrates that antenatal hypoxic stress can induce a continuum of responses depending on the species examined. Fetuses and newborns of certain species and specific human populations are well acclimated to antenatal hypoxia. However, antenatal hypoxia causes pulmonary vascular disease in fetuses and newborns of most mammalian species and humans. Disease can range from mild pulmonary hypertension, to severe vascular remodeling and dangerous elevations in pressure. The timing, length, and magnitude of the intrauterine hypoxic stress are important to disease development, however there is also a genetic-environmental relationship that is not yet completely understood. Determining the origins of pulmonary vascular remodeling and pulmonary hypertension and their associated effects is a challenging task, but is necessary in order to develop targeted therapies for pulmonary hypertension in the newborn due to antenatal hypoxia that can both treat the symptoms and curtail or reverse disease progression.

Hydrogen sulfide and translational medicine

Hydrogen sulfide (H2S) along with carbon monoxide and nitric oxide is an important signaling molecule that has undergone large numbers of fundamental investigations. H2S is involved in various physiological activities associated with the regulation of homeostasis, vascular contractility, pro- and anti-inflammatory activities, as well as pro- and anti-apoptotic activities etc. However, the actions of H2S are influenced by its concentration, reaction time, and cell/disease types. Therefore, H2S is a signaling molecule without definite effect. The use of existing H2S donors is limited because of the instant release and short lifetime of H2S. Thus, translational medicine involving the sustained and controlled release of H2S is of great value for both scientific and clinical uses. H2S donation can be manipulated by different ways, including where H2S is given, how H2S is donated, or the specific structures of H2S-releasing drugs and H2S donor molecules. This review briefly summarizes recent progress in research on the physiological and pathological functions of H2S and H2S-releasing drugs, and suggests hope for future investigations.

H2 S inhibits the activation of hepatic stellate cells and downregulates the expression of urotensin II

AIM

H2 S, a newly discovered signaling gasotransmitter, has been found involved in the pathogenesis of portal hypertension through the H2 S/CSE system. Studies also showed that urotensin II (UII), a recently discovered most potent vasoconstrictor, played an important role in cirrhotic portal hypertension. Therefore, studies were conducted to explore the relationship between H2 S and UII in cirrhosis.

METHODS

In the present study, the changes in the expression levels of cystathionine-γ-lyase (CSE), UII, urotensin II receptor (UT), collagen I, collagen III, tissue inhibitor of metalloproteinase-1 (TIMP-1) and α-smooth muscle actin (α-SMA) were determined by fluorescence quantitative polymerase chain reaction after exposure of hepatic stellate cells to H2 S. The influence of H2 S on UII was examined by western blotting, and the relationship between H2 S and UII was further confirmed by detection of cell proliferation and apoptosis.

RESULTS

Studies have shown that increase in H2 S concentration could reduce the expression of UII, UT, collagen I, collagen III, TIMP-1 and α-SMA without involvement of CSE. Moreover, the results of western blotting further proved that H2 S inhibited the expression of UII. The examination of cell proliferation by 5-ethynyl-2'-deoxyuridine assay suggests that H2 S significantly inhibited the proliferation of LX-2 cells and the proliferation-promoting effect of UII. Similarly, the examination of cell apoptosis revealed that H2 S could promote LX-2 cell apoptosis and inhibit the apoptosis-inhibiting effect of UII.

CONCLUSION

H2 S suppresses fibrosis by inhibiting the activation of hepatic stellate cells and reducing the expression of UII.

H2S: a "double face" molecule in health and disease

H2S is a colorless, poisonous, and flammable gas with the characteristic foul odor of rotten eggs. H2S is present in effluent from hydrothermal vents and sulfur springs, which have been proposed to act as "pores" in the Earth surface, providing a source of energy in the form of reducing equivalents and of iron-sulfur centers. Remarkably, H2S-producing machineries or H2S-utilization capacity remain within a great diversity of microorganisms. In particular, two classes of bacteria have been identified, that is, sulfate- and sulfur-reducing and sulfur-oxidizing bacteria, both contributing to the balance of the H2S level. The human body produces H2S and uses it as a signaling molecule in several physiological processes. However, many diseases, including neurological diseases, cardiovascular diseases, inflammation, and metabolic disorders, have been linked to abnormal endogenous H2S functions and metabolism. Remarkably, in recent years, the therapeutic administration of H2S(-donors) appears relevant in the treatment of some diseases. Here, H2S metabolism, as well as its physiological and pathological roles in humans is reviewed. Furthermore, the therapeutic use of H2S is discussed.

The role of endogenous H2S formation in reversible remodeling of lung tissue during hibernation in the Syrian hamster

During hibernation, small mammals alternate between periods of metabolic suppression and low body temperature ('torpor') and periods of full metabolic recovery with euthermic temperatures ('arousal'). Previously, we demonstrated marked structural remodeling of the lung during torpor, which is rapidly reversed during arousal. We also found that cooling of hamster cells increased endogenous production of H(2)S through the enzyme cystathionine-β-synthase (CBS). H(2)S suppresses the immune response and increases deposition of collagen. Therefore, we examined inflammatory markers and matrix metalloproteinase (MMP) activity in relation to CBS expression and H(2)S levels in lungs of euthermic and hibernating Syrian hamsters. Lung remodeling during torpor was confirmed by a strong increase in both collagenous and non-collagenous hydroxyproline content. The number of leukocytes in lung was unchanged in any phase of hibernation, while adhesion molecules VCAM-1 and ICAM-1, and the inflammatory marker NF-κB (P65) were modestly upregulated in torpor. Gelatinase activity was decreased in lungs from torpid animals, indicating inhibition of the Zn(2+)-dependent MMP-2 and MMP-9. Moreover, expression of CBS and tissue levels of H(2)S were increased in torpor. All changes normalized during arousal. Inhibition of gelatinase activity in torpor is likely caused by quenching of Zn(2+) by the sulphide ion of H(2)S. In accord, inhibition of CBS normalized gelatinase activity in torpid animals. Conversely, NaHS decreased the gelatinase activity of euthermic animals, which was attenuated by excess Zn(2+). Similar results were obtained on the activity of the Zn(2+)-dependent angiotensin converting enzyme. Our data indicate that increased production of H(2)S through CBS in hamster lungs during torpor contributes to remodeling by inhibition of gelatinase activity and possibly by suppression of the inflammatory response. Although administration of H(2)S is known to induce metabolic suppression in non-hibernating mammals ('suspended animation'), this is the first report implying endogenous H(2)S production in natural hibernation.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Correlation between serum H2S and pulmonary function in children with bronchial asthma

Endogenous hydrogen sulfide (H2S) has generated recent research interest because of its potential function as an inflammatory mediator. Despite its apparent functions in vascular smooth muscle, an important player in airway remodeling in asthma, little research has been done to assess the role of H2S in the pathogenesis of asthma. To determine whether serum H2S concentration is correlated with pulmonary function in children with asthma, we measured serum H2S concentration and pulmonary function indices (FVC, FEV1, PEF, FEF25-75, MEF50 and MEF25) in 64 children with asthma and 60 healthy children. Pearson's correlation was used to determine the relationship between serum H2S concentration and lung function parameters. Compared to healthy children, both serum H2S concentration and all lung function parameters were significantly decreased in children with asthma (P<0.05). Furthermore, serum H2S concentration was positively correlated with lung function indices (P<0.05). Thus, decreasing levels of H2S in the serum may be used to indicate decreasing lung function. Further investigation into the causality behind these findings is required.

The message in the air: hydrogen sulfide metabolism in chronic respiratory diseases

Hydrogen sulfide (H(2)S) is an important gasotransmitter in the mammalian respiratory system. The enzymes that produce H(2)S - mainly cystathionine-β-synthase and cystathionine-γ-lyase - are expressed in pulmonary and airway tissues. Endogenous H(2)S participates in the regulation of the respiratory system's physiological functions and pathophysiological alterations, such as chronic obstructive pulmonary disease, asthma, pulmonary fibrosis and hypoxia-induced pulmonary hypertension, to name a few. The cellular targets of H(2)S in the respiratory system are diverse, including airway smooth muscle cells, epithelial cells, fibroblasts, and pulmonary artery smooth muscle cells. H(2)S also regulates respiratory functions such as airway constriction, pulmonary circulation, cell proliferation or apoptosis, fibrosis, oxidative stress, and neurogenic inflammation. Cross-talk between H(2)S and other gasotransmitters also affects the net outcome of lung function. The metabolism of H(2)S in the lungs and airway may serve as a biomarker for specific respiratory diseases. It is expected that strategies targeted at the metabolism and function of H(2)S will prove useful for the prevention and treatment of selective chronic respiratory diseases.

Emerging role of hydrogen sulfide in health and disease: critical appraisal of biomarkers and pharmacological tools

H2S (hydrogen sulfide) is a well known and pungent gas recently discovered to be synthesized enzymatically in mammalian and human tissues. In a relatively short period of time, H2S has attracted substantial interest as an endogenous gaseous mediator and potential target for pharmacological manipulation. Studies in animals and humans have shown H2S to be involved in diverse physiological and pathophysiological processes, such as learning and memory, neurodegeneration, regulation of inflammation and blood pressure, and metabolism. However, research is limited by the lack of specific analytical and pharmacological tools which has led to considerable controversy in the literature. Commonly used inhibitors of endogenous H2S synthesis have been well known for decades to interact with other metabolic pathways or even generate NO (nitric oxide). Similarly, commonly used H2S donors release H2S far too quickly to be physiologically relevant, but may have therapeutic applications. In the present review, we discuss the enzymatic synthesis of H2S and its emerging importance as a mediator in physiology and pathology. We also critically discuss the suitability of proposed 'biomarkers' of H2S synthesis and metabolism, and highlight the complexities of the currently used pharmacological H2S 'donor' molecules and 'specific' H2S synthesis inhibitors in their application to studying the role of H2S in human disease.

Homocysteine to hydrogen sulfide or hypertension

Hyperhomocysteinemia, an increased level of plasma homocysteine, is an independent risk factor for the development of premature arterial fibrosis with peripheral and cerebro-vascular, neurogenic and hypertensive heart disease, coronary occlusion and myocardial infarction, as well as venous thromboembolism. It is reported that hyperhomocysteinemia causes vascular dysfunction by two major routes: (1) increasing blood pressure and, (2) impairing the vasorelaxation activity of endothelial-derived nitric oxide. The homocysteine activates metalloproteinases and induces collagen synthesis and causes imbalances of elastin/collagen ratio which compromise vascular elastance. The metabolites from hyperhomocysteinemic endothelium could modify components of the underlying muscle cells, leading to vascular dysfunction and hypertension. Homocysteine metabolizes in the body to produce H(2)S, which is a strong antioxidant and vasorelaxation factor. At an elevated level, homocysteine inactivates proteins by homocysteinylation including its endogenous metabolizing enzyme, cystathionine gamma-lyase. Thus, reduced production of H(2)S during hyperhomocysteinemia exemplifies hypertension and vascular diseases. In light of the present information, this review focuses on the mechanism of hyperhomocysteinemia-associated hypertension and highlights the novel modulatory role of H(2)S to ameliorate hypertension.

Role of urotensin II in health and disease

Urotensin II (UII) is an 11 amino acid cyclic peptide originally isolated from the goby fish. The amino acid sequence of UII is exceptionally conserved across most vertebrate taxa, sharing structural similarity to somatostatin. UII binds to a class of G protein-coupled receptor known as GPR14 or the urotensin receptor (UT). UII and its receptor, UT, are widely expressed throughout the cardiovascular, pulmonary, central nervous, renal, and metabolic systems. UII is generally agreed to be the most potent endogenous vasoconstrictor discovered to date. Its physiological mechanisms are similar in some ways to other potent mediators, such as endothelin-1. For example, both compounds elicit a strong vascular smooth muscle-dependent vasoconstriction via Ca2+ release. UII also exerts a wide range of actions in other systems, such as proliferation of vascular smooth muscle cells, fibroblasts, and cancer cells. It also 1) enhances foam cell formation, chemotaxis of inflammatory cells, and inotropic and hypertrophic effects on heart muscle; 2) inhibits insulin release, modulates glomerular filtration, and release of catecholamines; and 3) may help regulate food intake and the sleep cycle. Elevated plasma levels of UII and increased levels of UII and UT expression have been demonstrated in numerous diseased conditions, including hypertension, atherosclerosis, heart failure, pulmonary hypertension, diabetes, renal failure, and the metabolic syndrome. Indeed, some of these reports suggest that UII is a marker of disease activity. As such, the UT receptor is emerging as a promising target for therapeutic intervention. Here, a concise review is given on the vast physiologic and pathologic roles of UII.

Making and working with hydrogen sulfide: The chemistry and generation of hydrogen sulfide in vitro and its measurement in vivo: a review

Hydrogen sulfide is rapidly emerging as an important vasoactive mediator formed in health and disease. Its biological action is centered on its reactivity with heme-proteins and its ability to activate K(ATP) channels. Hydrogen sulfide is a signalling molecule of the inflammatory and nervous systems, and in particular the cardiovascular system where it regulates vascular tone, cardiac work, and exerts cardioprotection. This has led to an explosion of papers in which the role of hydrogen sulfide generated in vitro has been used to stimulate biological responses, and where a variety of methods have been used to measure the concentration of this compound in biological fluids. Understanding the chemistry and the inherent problems in the analytical techniques used to measure hydrogen sulfide concentrations is critical to our expanding knowledge on the biology of hydrogen sulfide. In this brief review we will cover the chemistry of hydrogen sulfide, including sources of hydrogen sulfide, its speciation at physiological pH, the susceptibility of sulfide to aerobic oxidation, and the methods used to measure hydrogen sulfide concentrations in solution, including biological fluids. We also give a brief overview of knockout animals and inhibition of the enzymes involved in the formation of hydrogen sulfide in vivo.

Hydrogen sulfide attenuates epithelial-mesenchymal transition of human alveolar epithelial cells

We previously reported that the endogenous cystathionine gamma-lyase (CSE)/hydrogen sulfide (H(2)S) pathway is implicated in the pathogenesis of bleomycin-induced pulmonary fibrosis in rats, but the exact cellular mechanisms are not well characterized. Epithelial-mesenchymal transition (EMT), induced by transforming growth factor beta1 (TGF-beta1) in alveolar epithelial cells, plays an important role in the pathogenesis of pulmonary fibrosis. We studied whether H(2)S could attenuate EMT in cultured alveolar epithelial cells and TGF-beta1 treatment suppressed CSE expression in A549 cells. Inhibition of endogenous CSE by dl-propargylglycine led to spontaneous EMT, as manifested by decreased E-cadherin level, increased vimentin expression and fibroblast-like morphologic features. Exogenous H(2)S applied to TGF-beta1-treated A549 cells decreased vimentin expression, increased E-cadherin level and retained epithelial morphologic features. In addition, preincubation with H(2)S decreased Smad2/3 phosphorylation in A549 cells stimulated by TGF-beta1, and H(2)S-inhibited alveolar EMT was mimicked by treatment with SB505124, a Smad2/3 inhibitor, but not pinacidil, an ATP-sensitive K(+) channel (K(ATP)) opener. H(2)S serves a critical role in preserving an epithelial phenotype and in attenuating EMT in alveolar epithelial cells, mediated, at least in part, by decreased Smad2/3 phosphorylation and not dependent on K(ATP) channel opening.

Role of hydrogen sulfide in the pathogenesis of cirrhotic portal hypertension

Gas signal molecules, such as hydrogen sulfide (H₂S), nitric oxide and carbon monoxide, play an important role in the regulation of physiology and pathophysiology of the human body. In this article, we will review the role of H₂S in the pathogenesis of cirrhotic portal hypertension. Besides, we will also discuss new treatment strategies for cirrhotic portal hypertension.

Hydrogen sulfide suppresses migration, proliferation and myofibroblast transdifferentiation of human lung fibroblasts

We previously reported that hydrogen sulfide (H(2)S) was implicated in the pathogenesis of bleomycin-induced pulmonary fibrosis in rat, but the cellular mechanisms underlying the role it played were not well characterized. The present study was undertaken to investigate the role of the exogenous H(2)S in human lung fibroblast (MRC5) migration, proliferation and myofibroblast transdifferentiation induced by fetal bovine serum (FBS) and growth factors in vitro, to elucidate the mechanisms by which H(2)S inhibits pathogenesis of pulmonary fibrosis. We found that H(2)S incubation significantly decreased the MRC5 cell migration distance stimulated by FBS and basic fibroblast growth factor (bFGF), inhibited MRC5 cell proliferation induced by FBS and platelet-derived growth factor-BB (PDGF-BB), and also inhibited transforming growth factor-beta1 (TGF-beta1) induced MRC5 cell transdifferentiation into myofibroblasts. Moreover, preincubation with H(2)S decreased extracellular signal-regulated kinase (ERK1/2) phosphorylation in MRC5 cells induced by FBS, PDGF-BB, TGF-beta1, and bFGF. However, the inhibition effects of H(2)S on MRC5 cell migration, proliferation and myofibroblast transdifferentiation were not attenuated by glibenclamide, an ATP-sensitive K(+) channel (K(ATP)) blocker. Thus, H(2)S directly suppressed fibroblast migration, proliferation and phenotype transform stimulated by FBS and growth factors in vitro, which suggests that it could be an important mechanism of H(2)S-suppressed pulmonary fibrosis. These effects of H(2)S on pulmonary fibroblasts were, at least in part, mediated by decreased ERK phosphorylation and were not dependent on K(ATP) channel opening.