Hydrogen sulfide: from brain to gut

Real-Time Monitoring of Air Pollution Health Impacts Using Breath-Borne Gaseous Biomarkers from Rats

Offline techniques are adopted for studying air pollution health impacts, thus failing to provide in situ observations. Here, we have demonstrated their real-time monitoring by online analyzing an array of gaseous biomarkers from rats' exhaled breath using an integrated exhaled breath array sensor (IEBAS) developed. The biomarkers include total volatile organic compounds (TVOC), CO2, CO, NO, H2S, H2O2, O2, and NH3. Specific breath-borne VOCs were also analyzed by a gas chromatography-ion mobility spectrometer (GC-IMS). After real-life ambient air pollution exposures (2 h), the pollution levels of PM2.5 and O3 were both found to significantly affect the relative levels of multiple gaseous biomarkers in rats' breath. Eleven biomarkers, especially NO, H2S, and 1-propanol, were detected as significantly correlated with PM2.5 concentration, while heptanal was shown to be significantly correlated with O3. Likewise, significant changes were also detected in multiple breath-borne biomarkers from rats under lab-controlled O3 exposures with levels of 150, 300, and 1000 μg/m3 (2 h), compared to synthetic air exposure. Importantly, heptanal was experimentally confirmed as a reliable biomarker for O3 exposure, with a notable dose-response relationship. In contrast, conventional biomarkers of inflammation and oxidative stress in rat sera exhibited insignificant differences after the 2 h exposures. The results imply that breath-borne gaseous biomarkers can serve as an early and sensitive indicator for ambient pollutant exposure. This work pioneered a new research paradigm for online monitoring of air pollution health impacts while obtaining important candidate biomarker information for PM2.5 and O3 exposures.

Hydrogen sulfide donors across time: From origins to cutting-edge applications

This review aims to analyze the developmental trajectory of hydrogen sulfide (H2S) donors over the past three decades and explore the historical background, research hotspots, and emerging trends in related fields from a temporal perspective. A total of 5092 literature articles on H2S donors were retrieved from the Web of Science Core Collection (WoSCC), encompassing 1303 journals, 20638 authors, 10992 institutions, and 459 countries and regions. Utilizing CiteSpace as a bibliometric tool, historical features, evolving active topics, and emerging trends in the field of H2S donors were identified. Over the past 30 years, the field of H2S donors has remained in a prominent stage. This article discusses both inorganic and organic types of H2S donors, including NaHS and Na2S, GYY4137, AP39, and AP123, as well as briefly outlines research and applications of H2S donors in nanotechnology, advanced materials, composite materials, nanostructures, and optical properties. Mechanistically, the review outlines how H2S donors regulate cellular signal transduction, anti-inflammatory responses, neuroprotection, and other pathways within the organism by modulating protein S-sulfhydration, antioxidant effects, and interactions with metal proteins. In terms of applications, the review summarizes the extensive use of H2S donors in biomedical research, encompassing cardiovascular, neurological, anti-inflammatory, and anti-cancer characteristics, as well as their potential applications in the treatment of metabolic diseases. Finally, challenges and limitations faced by H2S donor research are discussed, and potential future research directions are proposed.

Hydrogen Sulfide: Physiological Roles and Therapeutic Implications against COVID-19

The COVID-19 pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) poses a major menace to economic and public health worldwide. Angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) are two host proteins that play an essential function in the entry of SARS-- COV-2 into host cells. Hydrogen sulfide (H2S), a new gasotransmitter, has been shown to protect the lungs from potential damage through its anti-inflammatory, antioxidant, antiviral, and anti-aging effects. It is well known that H2S is crucial in controlling the inflammatory reaction and the pro-inflammatory cytokine storm. Therefore, it has been suggested that some H2S donors may help treat acute lung inflammation. Furthermore, recent research illuminates a number of mechanisms of action that may explain the antiviral properties of H2S. Some early clinical findings indicate a negative correlation between endogenous H2S concentrations and COVID-19 intensity. Therefore, reusing H2S-releasing drugs could represent a curative option for COVID-19 therapy.

Reduced hydrogen sulfide production contributes to adrenal insufficiency induced by hypoxia via modulation of NLRP3 inflammasome activation

Objective: Adrenocortical responsiveness is critical for maintaining glucocorticoids production and homeostasis during stress. We sought to investigate adrenocortical responsiveness during hypoxia in mice and the mechanisms responsible for the regulation of adrenal responsiveness.Methods: (1) Adult male WT mice were randomly divided into four groups: normoxia, hypoxia (24h), hypoxia (72h), hypoxia (72h) + GYY4137(hydrogen sulfide (H₂S) donor, 133mmol/kg/day); (2) WT mice were randomly divided into four groups: sham, adrenalectomy (ADX), sham+hypoxia, ADX+hypoxia; (3) Cse^-/- mice were randomly divided into two groups: Cse^-/-, Cse^-/- +GYY4137.Results: The circulatory level of corticosteroid induced by ACTH stimulation was significantly reduced in the mice with hypoxia compared with control mice. The mortality rate induced by lipopolysaccharide (LPS) increased during hypoxia. Cystathionine-γ-lyase (CSE) expression was significantly reduced in adrenal glands during hypoxia. GYY4137 treatment significantly increased adrenal responsiveness and attenuated NLRP3 inflammasome activation in mice treated by hypoxia and Cse^-/- mice. Furthermore, The sulfhydrated level of PSMA7 in adrenal gland was decreased in the mice with hypoxia and Cse^-/- mice. PSMA7 was S-sulfhydrated at cysteine 70. Blockage of S-sulfhydration of PSMA7 increased NLRP3 expression in adrenocortical cells.Conclusion: Reduced H₂S production mediated hypo-adrenocortical responsiveness and NLRP3 inflammasome activation via PAMA7 S-sulfhydration during hypoxia.

Hydrogen sulfide inhibits gene expression associated with aortic valve degeneration by inducing NRF2-related pro-autophagy effect in human aortic valve interstitial cells

Aortic valve stenosis (AS) is the most common valvular heart disease but there are currently no effective medical treatments that can delay disease progression due to a lack of knowledge of the precise pathophysiology. The expression of sulfide: quinone oxidoreductase (SQOR) and nuclear factor erythroid 2-related factor 2 (NRF2) was decreased in the aortic valve of AS patients. However, the role of SQOR and NRF2 in the pathophysiology of AS has not been found. We investigated the effects of hydrogen sulfide (H2S)-releasing compounds on diseased aortic valve interstitial cells (AVICs) to explain the cellular mechanism of SQOR and elucidate the medical value of H2S for AS treatment. Sodium hydrosulfide (NaHS) treatment increased the expression of SQOR and NRF2 gene and consequently induced the NRF2 target genes, such as NAD(P)H quinone dehydrogenase 1 and cystathionine γ-lyase. In addition, NaHS dose-dependently decreased the expression level of fibrosis and inflammation-related genes (MMP9, TNF-α, IL6) and calcification-related genes (ALP, osteocalcin, RUNX2, COL1A1) in human AVICs. Furthermore, NaHS activated the AMPK-mTOR pathway and inhibited the PI3K-AKT pathway, resulting in a pro-autophagy effect in human AVICs. An NRF2 inhibitor, brusatol, attenuated NaHS-induced AMPK activation and decreased the autophagy markers Beclin-1 and LC3AB, suggesting that the mechanism of action of H2S is related to NRF2. In conclusion, H2S decreased gene expression levels related to aortic valve degeneration and activated AMPK-mTOR-mediated pro-autophagy function associated with NRF2 in human AVICs. Therefore, H2S could be a potential therapeutic target for the development of AS treatment.

The double-edged sword role of hydrogen sulfide in hepatocellular carcinoma

With an increasing worldwide prevalence, hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver in the world. It is also the primary reason for cancer-related death in the world. The pathogenesis of HCC is complex, such as DNA methylation changes, immune regulatory disorders, cell cycle disorders, chromosomal instability, and so on. Although many studies have been conducted on HCC, the molecular mechanisms of HCC are not completely understood. At present, there is no effective treatment for HCC. Hydrogen sulfide (H2S) has long been regarded as a toxic gas with the smell of rotten eggs, but recent studies have shown that it is an important gasotransmitter along with carbon monoxide (CO) and nitric oxide (NO). Increasing evidence indicates that H2S has multiple biological functions, such as anti-inflammation, anti-apoptosis, anti-oxidative stress, and so on. Recently, a lot of evidence has shown that H2S has a "double-edged sword" effect in HCC, but the mechanism is not fully understood. Here, we reviewed the progress on the role and mechanism of H2S in HCC in recent years, hoping to provide a theoretical reference for future related research.

Development of a H2S-responsive NIR Fluorescent Probe for H2S Detection and H2S Releasing Monitoring From Prodrug

H2S was deemed as a toxic gradient in the realm of food and environment but plays pivotal pathophysiological roles in organisms. H2S instabilities and disturbances are always responsible for multiple disorders. We fabricated a H2S-responsive NIR fluorescent probe (HT) for H2S detection and evaluation both in vitro and in vivo. HT exhibited rapid H2S response within 5 min, accompanied with visible color change and NIR fluorescence generation, and the fluorescent intensities were linearly correlated with corresponding H2S concentrations. When HT was incubated with A549 cells, the intracellular H2S and H2S fluctuations could be monitored ore rotundo via the responsive fluorescence. Meanwhile, when HT was co-administrated with H2S prodrug ADT-OH, the H2S release from ADT-OH could be visualized and monitored to evaluate its release efficacy.

Inhibition of the voltage-gated potassium channel Kv1.5 by hydrogen sulfide attenuates remodeling through S-nitrosylation-mediated signaling

The voltage-gated K+ channel plays a key role in atrial excitability, conducting the ultra-rapid rectifier K+ current (IKur) and contributing to the repolarization of the atrial action potential. In this study, we examine its regulation by hydrogen sulfide (H2S) in HL-1 cardiomyocytes and in HEK293 cells expressing human Kv1.5. Pacing induced remodeling resulted in shorting action potential duration, enhanced both Kv1.5 channel and H2S producing enzymes protein expression in HL-1 cardiomyocytes. H2S supplementation reduced these remodeling changes and restored action potential duration through inhibition of Kv1.5 channel. H2S also inhibited recombinant hKv1.5, lead to nitric oxide (NO) mediated S-nitrosylation and activated endothelial nitric oxide synthase (eNOS) by increased phosphorylation of Ser1177, prevention of NO formation precluded these effects. Regulation of Ikur by H2S has important cardiovascular implications and represents a novel and potential therapeutic target.

Microbial metabolites in the pathogenesis of periodontal diseases: a narrative review

The purpose of this narrative review is to highlight the importance of microbial metabolites in the pathogenesis of periodontal diseases. These diseases, involving gingivitis and periodontitis are inflammatory conditions initiated and maintained by the polymicrobial dental plaque/biofilm. Gingivitis is a reversible inflammatory condition while periodontitis involves also irreversible destruction of the periodontal tissues including the alveolar bone. The inflammatory response of the host is a natural reaction to the formation of plaque and the continuous release of metabolic waste products. The microorganisms grow in a nutritious and shielded niche in the periodontal pocket, protected from natural cleaning forces such as saliva. It is a paradox that the consequences of the enhanced inflammatory reaction also enable more slow-growing, fastidious, anaerobic bacteria, with often complex metabolic pathways, to colonize and thrive. Based on complex food chains, nutrient networks and bacterial interactions, a diverse microbial community is formed and established in the gingival pocket. This microbiota is dominated by anaerobic, often motile, Gram-negatives with proteolytic metabolism. Although this alternation in bacterial composition often is considered pathologic, it is a natural development that is promoted by ecological factors and not necessarily a true "dysbiosis". Normal commensals are adapting to the gingival crevice when tooth cleaning procedures are absent. The proteolytic metabolism is highly complex and involves a number of metabolic pathways with production of a cascade of metabolites in an unspecific manner. The metabolites involve short chain fatty acids (SCFAs; formic, acetic, propionic, butyric, and valeric acid), amines (indole, scatole, cadaverine, putrescine, spermine, spermidine) and gases (NH₃, CO, NO, H₂S, H₂). A homeostatic condition is often present between the colonizers and the host response, where continuous metabolic fluctuations are balanced by the inflammatory response. While it is well established that the effect of the dental biofilm on the host response and tissue repair is mediated by microbial metabolites, the mechanisms behind the tissue destruction (loss of clinical attachment and bone) are still poorly understood. Studies addressing the functions of the microbiota, the metabolites, and how they interplay with host tissues and cells, are therefore warranted.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Advances of H2S in Regulating Neurodegenerative Diseases by Preserving Mitochondria Function

Neurotoxicity is induced by different toxic substances, including environmental chemicals, drugs, and pathogenic toxins, resulting in oxidative damage and neurodegeneration in mammals. The nervous system is extremely vulnerable to oxidative stress because of its high oxygen demand. Mitochondria are the main source of ATP production in the brain neuron, and oxidative stress-caused mitochondrial dysfunction is implicated in neurodegenerative diseases. H2S was initially identified as a toxic gas; however, more recently, it has been recognized as a neuromodulator as well as a neuroprotectant. Specifically, it modulates mitochondrial activity, and H2S oxidation in mitochondria produces various reactive sulfur species, thus modifying proteins through sulfhydration. This review focused on highlighting the neuron modulation role of H2S in regulating neurodegenerative diseases through anti-oxidative, anti-inflammatory, anti-apoptotic and S-sulfhydration, and emphasized the importance of H2S as a therapeutic molecule for neurological diseases.

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.

D-cysteine ethyl ester and D-cystine dimethyl ester reverse the deleterious effects of morphine on arterial blood-gas chemistry and Alveolar-arterial gradient in anesthetized rats

We determined whether intravenous injections of the membrane-permeable ventilatory stimulants, D-cysteine ethyl ester (ethyl (2 S)– 2-amino-3-sulfanylpropanoate) (D-CYSee) and D-cystine dimethyl ester (methyl (2 S)– 2-amino-3-[[(2 S)– 2-amino-3-methoxy-3-oxopropyl]disulfanyl] propanoate) (D-CYSdime), could overcome the deleterious actions of intravenous morphine on arterial blood pH, pCO₂, pO₂ and sO₂, and Alveolar-arterial (A-a) gradient (i.e., the measure of exchange of gases in the lungs) in Sprague Dawley rats anesthetized with isoflurane. Injection of morphine (2 mg/kg, IV) caused pronounced reductions in pH, pO₂ and sO₂ accompanied by elevations in pCO₂, all which are suggestive of diminished ventilation, and elevations in A-a gradient, which suggests a mismatch of ventilation-perfusion. Subsequent boluses of D-cysteine ethyl ester (2 × 100 μmol/kg, IV) or D-cystine dimethyl ester (2 ×50 μmol/kg, IV) rapidly reversed of the negative actions of morphine on pH, pCO₂, pO₂ and sO₂, and A-a gradient. Similar injections of D-cysteine (2 × 100 μmol/kg, IV) were without effect, whereas injections of D-cystine (2 × 50 μmol/kg, IV) produced a modest reversal. Our data show that D-cysteine ethyl ester and D-cystine dimethyl ester readily overcome the deleterious effects of morphine on arterial blood gas (ABG) chemistry and A-a gradient by mechanisms that may depend upon their ability to rapidly enter cells. As a result of their known ability to enter the brain, lungs, muscles of the chest wall, and most likely the major peripheral chemoreceptors (i.e., carotid bodies), the effects of the thiolesters on changes in ABG chemistry and A-a gradient elicited by morphine likely involve central and peripheral mechanisms. We are employing target prediction methods to identify an array of in vitro and in vivo methods to test potential functional proteins by which D-CYSee and D-CYSdime modulate the effects of morphine on breathing.

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

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

Exploring Thermal Sensitivities and Adaptations of Oxidative Phosphorylation Pathways

Temperature shifts are a major challenge to animals; they drive adaptations in organisms and species, and affect all physiological functions in ectothermic organisms. Understanding the origin and mechanisms of these adaptations is critical for determining whether ectothermic organisms will be able to survive when faced with global climate change. Mitochondrial oxidative phosphorylation is thought to be an important metabolic player in this regard, since the capacity of the mitochondria to produce energy greatly varies according to temperature. However, organism survival and fitness depend not only on how much energy is produced, but, more precisely, on how oxidative phosphorylation is affected and which step of the process dictates thermal sensitivity. These questions need to be addressed from a new perspective involving a complex view of mitochondrial oxidative phosphorylation and its related pathways. In this review, we examine the effect of temperature on the commonly measured pathways, but mainly focus on the potential impact of lesser-studied pathways and related steps, including the electron-transferring flavoprotein pathway, glycerophosphate dehydrogenase, dihydroorotate dehydrogenase, choline dehydrogenase, proline dehydrogenase, and sulfide:quinone oxidoreductase. Our objective is to reveal new avenues of research that can address the impact of temperature on oxidative phosphorylation in all its complexity to better portray the limitations and the potential adaptations of aerobic metabolism.

Hydrogen sulfide-induced post-translational modification as a potential drug target

Hydrogen sulfide (H₂S) is one of the three known gas signal transducers, and since its potential physiological role was reported, the literature on H₂S has been increasing. H₂S is involved in processes such as vasodilation, neurotransmission, angiogenesis, inflammation, and the prevention of ischemia-reperfusion injury, and its mechanism remains to be further studied. At present, the role of post-translational processing of proteins has been considered as a possible mechanism for the involvement of H₂S in a variety of physiological processes. Current studies have shown that H₂S is involved in S-sulfhydration, phosphorylation, and S-nitrosylation of proteins, etc. This paper focuses on the effects of protein modification involving H₂S on physiological and pathological processes, looking forward to providing guidance for subsequent research.

Chemiluminescence Measurement of Reactive Sulfur and Nitrogen Species

Significance: Reactive sulfur and nitrogen species such as hydrogen sulfide (H₂S) and nitric oxide (NO^•) are ubiquitous cellular signaling molecules that play central roles in physiology and pathophysiology. A deeper understanding of these signaling pathways will offer new opportunities for therapeutic treatments and disease management. Recent Advances: Chemiluminescence methods have been fundamental in detecting and measuring biological reactive sulfur and nitrogen species, and new approaches are emerging for imaging these analytes in living intact specimens. Ozone-based and luminol-based chemiluminescence methods have been optimized for quantitative analysis of hydrogen sulfide and nitric oxide in biological samples and tissue homogenates, and caged luciferin and 1,2-dioxetanes are emerging as a versatile approach for monitoring and imaging reactive sulfur and nitrogen species in living cells and animal models. Critical Issues: This review article will cover the major chemiluminescence approaches for detecting, measuring, and imaging reactive sulfur and nitrogen species in biological systems, including a brief history of the development of the most established approaches and highlights of the opportunities provided by emerging approaches. Future Directions: Emerging chemiluminescence approaches offer new opportunities for monitoring and imaging reactive sulfur and nitrogen species in living cells, animals, and human clinical samples. Widespread adoption and translation of these approaches, however, requires an emphasis on rigorous quantitative methods, reproducibility, and effective technology transfer. Antioxid. Redox Signal. 36, 337-353.

Effects of Exogenous Hydrogen Sulfide in the Hypothalamic Paraventricular Nucleus on Gastric Function in Rats

Background: Hydrogen sulfide (H₂S) is a new type of gas neurotransmitter discovered in recent years. It plays an important role in various physiological activities. The hypothalamus paraventricular nucleus (PVN) is an important nucleus that regulates gastric function. This study aimed to clarify the role of H₂S in the paraventricular nucleus of the hypothalamus on the gastric function of rats.

Methods: An immunofluorescence histochemistry double-labelling technique was used to determine whether cystathionine-beta-synthase (CBS) and c-Fos neurons are involved in PVN stress. Through microinjection of different concentrations of NaHS, physiological saline (PS), D-2-Amino-5-phosphonovaleric acid (D-AP5), and pyrrolidine dithiocarbamate (PDTC), we observed gastric motility and gastric acid secretion.

Results: c-Fos and CBS co-expressed the most positive neurons after 1 h of restraint and immersion, followed by 3 h, and the least was at 0 h. After injection of different concentrations of NaHS into the PVN, gastric motility and gastric acid secretion in rats were significantly inhibited and promoted, respectively (p < 0.01); however, injection of normal saline, D-AP5, and PDTC did not cause any significant change (p > 0.05). The suppressive effect of NaHS on gastrointestinal motility and the promotional effect of NaHS on gastric acid secretion could be prevented by D-AP5, a specific N-methyl-D-aspartic acid (NMDA) receptor antagonist, and PDTC, an NF-κB inhibitor.

Conclusion: There are neurons co-expressing CBS and c-Fos in the PVN, and the injection of NaHS into the PVN can inhibit gastric motility and promote gastric acid secretion in rats. This effect may be mediated by NMDA receptors and the NF-κB signalling pathway.

The role of l-cysteine/Hydrogen sulfide pathway on β3-Adrenoceptor- induced relaxation in mouse gastric fundus

In this study, we investigated the possible role of the l-cysteine/hydrogen sulfide pathway in β₃-adrenoceptors-mediated relaxation in isolated mouse gastric fundus tissue. l-cysteine (endogenous H₂S; 10^-6-10^-2 M), sodium hydrogen sulfide (NaHS; exogenous H₂S; 10^-6-10^-3 M), selective β₃-adrenoceptors agonist BRL 37344 (10^-9-10^-4 M) and non-selective β-adrenoceptor agonist isoprenaline (10^-9-10^-4 M) produced concentration-dependent relaxation in mouse gastric fundus. The non-selective β-adrenoceptors antagonist propranolol (10^-6 M) inhibited the relaxant response to isoprenaline but not to BRL 37344. On the other hand, the selective β₃-adrenoceptors antagonist SR 59230A (10^-5 M) inhibited the relaxant responses to BRL 37344. In addition, cystathionine-gamma-lyase (CSE) inhibitor D,L-propargylglycine (PAG, 10^-2 M), cystathionine-beta-synthase inhibitor (CBS) aminooxyacetic acid (AOAA, 10^-2 M), and the combination of these inhibitors significantly reduced the relaxant responses induced by l-cysteine and BRL 37344. Pre-incubation of gastric fundal strips with propranolol (10^-6 M) and SR 59230A (10^-5 M) did not affect relaxations to l-cysteine and NaHS. Also, the existence of CSE, CBS, 3-mercaptopurivate sulfur transferase (3-MST) enzymes and β₃-adrenoceptors were detected in gastric fundal tissue. Furthermore, basal H₂S release was detected in the measurements. H₂S level increased in the presence of l-cysteine, NaHS, and BRL 37344. The increase in H₂S level by l-cysteine and BRL 37344 decreased significantly with PAG and AOAA enzyme inhibitors. These results suggest that endogenous H₂S is synthesized from l-cysteine at least by CBS and CSE enzymes. Also, β₃-adrenoceptors are found in the mouse stomach fundus and mediate BRL 37344-induced relaxations, and l-cysteine/hydrogen sulfide pathway plays a partial role in β₃-adrenoceptors-mediated relaxation in mouse gastric fundus tissue.

A phenothiazine-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in food, live cells and animals

In this work, a phenothiazine-based fluorescent probe (PR) has been developed for the selective detection of hydrogen sulfide (H₂S) in biosystems and monitoring H₂S produced in the food spoilage process. The nucleophilic attack of H₂S on the CC double bond of PRvia a Michael addition interdicted the ICT process to trigger 34-fold enhancement of the fluorescence emission. PR featured high selectivity and sensitivity (1.8 μM), low cytotoxicity and reliability at physiological pH. "Naked-eye" monitoring of H₂S produced in the food spoilage process using PR was successfully accomplished. The preliminary fluorescence imaging studies showed that PR is suitable for the visualization of exogenous and endogenous H₂S in living cells and live animals. Moreover, PR has been successfully applied to the visualization of H₂S generation in an inflammation model. The results indicated that PR is an effective tool to monitor H₂S production in the fields of biomedicine and food safety.

Sulfide and transition metals - A partnership for life

Sulfide and transition metals often came together in Biology. The variety of possible structural combinations enabled living organisms to evolve an array of highly versatile metal-sulfide centers to fulfill different physiological roles. The ubiquitous iron‑sulfur centers, with their structural, redox, and functional diversity, are certainly the best-known partners, but other metal-sulfide centers, involving copper, nickel, molybdenum or tungsten, are equally crucial for Life. This review provides a concise overview of the exclusive sulfide properties as a metal ligand, with emphasis on the structural aspects and biosynthesis. Sulfide as catalyst and as a substrate is discussed. Different enzymes are considered, including xanthine oxidase, formate dehydrogenases, nitrogenases and carbon monoxide dehydrogenases. The sulfide effect on the activity and function of iron‑sulfur, heme and zinc proteins is also addressed.

The Capacity to Produce Hydrogen Sulfide (H2S) via Cysteine Degradation Is Ubiquitous in the Human Gut Microbiome

As one of the three mammalian gasotransmitters, hydrogen sulfide (H₂S) plays a major role in maintaining physiological homeostasis. Endogenously produced H₂S plays numerous beneficial roles including mediating vasodilation and conferring neuroprotection. Due to its high membrane permeability, exogenously produced H₂S originating from the gut microbiota can also influence human physiology and is implicated in reducing intestinal mucosal integrity and potentiating genotoxicity and is therefore a potential target for therapeutic interventions. Gut microbial H₂S production is often attributed to dissimilatory sulfate reducers such as Desulfovibrio and Bilophila species. However, an alternative source for H₂S production, cysteine degradation, is present in some gut microbes, but the genes responsible for cysteine degradation have not been systematically annotated in all known gut microbes. We classify mechanisms of cysteine degradation into primary, secondary, and erroneous levels of H₂S production and perform a comprehensive search for primary, secondary, and erroneous cysteine-degrading enzymes in 4,644 non-redundant bacterial genomes from the Unified Human Gastrointestinal Genome (UHGG) catalog. Of the 4,644 genomes we have putatively identified 2,046 primary, 1,951 secondary, and 5 erroneous cysteine-degrading species. We identified the presence of at least one putative cysteine-degrading bacteria in metagenomic data of 100% of 6,623 healthy subjects and the expression of cysteine-degrading genes in metatranscriptomic data of 100% of 736 samples taken from 318 individuals. Additionally, putative cysteine-degrading bacteria are more abundant than sulfate-reducing bacteria across healthy controls, IBD patients and CRC patients (p < 2.2e-16, Wilcoxon rank sum test). Although we have linked many taxa with the potential for cysteine degradation, experimental validation is required to establish the H₂S production potential of the gut microbiome. Overall, this study improves our understanding of the capacity for H₂S production by the human gut microbiome and may help to inform interventions to therapeutically modulate gut microbial H₂S production.

Fluidics system for resolving concentration-dependent effects of dissolved gases on tissue metabolism

Oxygen (O2) and other dissolved gases such as the gasotransmitters H2S, CO, and NO affect cell metabolism and function. To evaluate effects of dissolved gases on processes in tissue, we developed a fluidics system that controls dissolved gases while simultaneously measuring parameters of electron transport, metabolism, and secretory function. We use pancreatic islets, retina, and liver from rodents to highlight its ability to assess effects of O2 and H2S. Protocols aimed at emulating hypoxia-reperfusion conditions resolved a previously unrecognized transient spike in O2 consumption rate (OCR) following replenishment of O2, and tissue-specific recovery of OCR following hypoxia. The system revealed both inhibitory and stimulatory effects of H2S on insulin secretion rate from isolated islets. The unique ability of this new system to quantify metabolic state and cell function in response to precise changes in dissolved gases provides a powerful platform for cell physiologists to study a wide range of disease states.

A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism

The ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H₂S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O₂ sensing mechanism. This hypothesis is based on observations that H₂S and RSS metabolism is inversely correlated with O₂ tension, exogenous H₂S elicits physiological responses identical to those produced by hypoxia, factors that affect H₂S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O₂. H₂S-mediated O₂ sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O₂ sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.

H2O2-Mediated Oxidative Stress Enhances Cystathionine γ-Lyase-Derived H2S Synthesis via a Sulfenic Acid Intermediate

Hydrogen sulfide (H₂S), which is generated mainly by cystathionine γ-lyase (CSE) in the cardiovascular system, plays a pivotal role in a wide range of physiological and pathological processes. However, the regulatory mechanism of the CSE/H₂S system is poorly understood. Herein, we show that oxidation induces the disulfide bond formation between Cys252 and Cys255 in the CXXC motif, thus stimulating the H₂S-producing activity of CSE. The activity of oxidized CSE is approximately 2.5 fold greater than that of the reduced enzyme. Molecular dynamics and molecular docking suggest that the disulfide bond formation induces the conformational change in the active site of CSE and consequently increases the affinity of the enzyme for the substrate L-cysteine. Mass spectrometry and mutagenesis studies further established that the residue Cys255 is crucial for oxidation sensing. Oxidative stress-mediated sulfenylation of Cys255 leads to a sulfenic acid intermediate that spontaneously forms an intramolecular disulfide bond with the vicinal thiol group of Cys252. Moreover, we demonstrate that exogenous hydrogen peroxide (H₂O₂) and endogenous H₂O₂ triggered by vascular endothelial growth factor (VEGF) promote cellular H₂S production through the enhancement of CSE activity under oxidative stress conditions. By contrast, incubation with H₂O₂ or VEGF did not significantly enhance cellular H₂S production in the presence of PEG-catalase, an enzymatic cell-permeable H₂O₂ scavenger with high H₂O₂ specificity. Taken together, we report a new posttranslational modification of CSE that provides a molecular mechanism for H₂O₂/H₂S crosstalk in cells under oxidative stress.

Accurate Fluorescence Diagnosis of Cancer Based on Sequential Detection of Hydrogen Sulfide and pH

Cancer ranks as a leading cause of death in every country of the world. However, if they are discovered early, a lot of cancers can be prevented or cured. Discovering and monitoring cancer markers are the main methods for early diagnosis of cancer. To date, many fluorescent probes designed and used for early cancer diagnosis can only react with a single marker, which always causes insufficient accuracy in complex systems. Herein, a novel near-infrared (NIR) fluorescent probe (CyO-DNP) for the sequential detection of H₂S and H⁺ is synthesized. In this probe, a heptamethine dye is selected as the fluorophore and a 2,4-dinitrophenyl (DNP) ether is chosen as recognition group. In the presence of H₂S, CyO-DNP is transformed into CyO, which exhibits an intense fluorescence at 663 nm. Then, H⁺ induces the protonation of CyO to obtain CyOH, and the final fluorescence emission at 793 nm significantly enhances. Owing to the low cytotoxicity and the NIR fluorescence emission, CyO-DNP can sequentially monitor endogenous H₂S and H⁺ in cancer cells and image exogenous and endogenous H₂S and H⁺ in mice. It is worth mentioning that CyO-DNP can effectively avoid the false positive signal caused by the liver and kidney and discriminate normal mice and tumor mice accurately. For all we know, CyO-DNP is the first fluorescent probe for early accurate diagnosis of cancer by sequentially detecting H₂S and H⁺.

The secretion of cytokines by peripheral blood mononuclear cells of patients with periodontitis and healthy controls when exposed to H2S

Background: Hydrogen sulfide(H₂S) is a bacterial metabolite produced as a result of bacterial growth in subgingival pockets, suggested to partake in the pathogenesis of periodontitis. H₂S has previously been shown to induce the secretion of the pro-inflammatory cytokines IL-1β and IL-18 via the NLRP3 inflammasome in monocytes.

Objective: To investigate the non-NLRP3 inflammasome-dependent immunological response of human peripheral blood mononuclear cells (PBMCs) of periodontitis patients and healthy controls exposed to H₂S in vitro.

Methods: PBMCs of periodontitis patients(N = 31) and healthy controls(N = 32) were exposed to 1 mM sodium hydrosulfide (NaHS) at 37°C for 24 h and the secretion of cytokines was compared to resting cells. TNF-α, IFN-γ, IL-6, IL-8, IL-12p40, IL-12p70, IL-17, MCP-1, and IL-1Ra secretions were measured with Bio-Plex Pro™ Human Cytokine Assay.

Results: H₂S triggered the secretion of the pro-inflammatory IFN-γ, IL-6, IL-17, TNF-α, IL-12p40, and IL-12p70, while the reverse was seen for IL-1Ra. In addition, a higher basal secretion of IFN-γ, IL-6, IL-12p70, IL-17 and MCP-1 was seen from PBMCs of periodontitis patients compared to healthy controls.

Conclusion: The bacterial metabolite H₂S triggers the secretion of pro-inflammatory cytokines from PBMCs and may thus have a prominent role in the host-bacteria interplay in periodontitis.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

Nutrition and sulfur

Sulfur is unusual in that it is a mineral that may be taken into the body in both inorganic and organic combinations. It has been available within the environment throughout the development of lifeforms and as such has become integrated into virtually every aspect of biochemical function. It is essential for the nature and maintenance of structure, assists in communication within the organism, is vital as a catalytic assistant in intermediary metabolism and the mechanism of energy flow as well as being involved in internal defense against potentially damaging reactive species and invading foreign chemicals. Recent studies have suggested extended roles for sulfur-containing molecules within living systems. As such, questions have been raised as to whether or not humans are receiving sufficient sulfur within their diet. Sulfur appears to have been the "poor relation" with regards to mineral nutrition. This may be because of difficulties encountered over its multifarious functions, the many chemical guises in which it may be ingested and its complex biochemical interconversions once taken into the body. No established daily requirements have been determined, unlike many minerals, although suggestions have been proposed. Owing to its widespread distribution within dietary components its intake has almost been taken for granted. In the majority of individuals partaking of a balanced diet the supply is deemed adequate, but those opting for specialized or restrictive diets may experience occasional and low-level shortages. In these instances, the careful use of sulfur supplements may be of benefit.

H2S protects hippocampal neurons against hypoxia-reoxygenation injury by promoting RhoA phosphorylation at Ser188

Inhibition of RhoA-ROCK pathway is involved in the H₂S-induced cerebral vasodilatation and H₂S-mediated protection on endothelial cells against oxygen-glucose deprivation/reoxygenation injury. However, the inhibitory mechanism of H₂S on RhoA-ROCK pathway is still unclear. The aim of this study was to investigate the target and mechanism of H₂S in inhibition of RhoA/ROCK. GST-RhoA^wild and GST-RhoA^S188A proteins were constructed and expressed, and were used for phosphorylation assay in vitro. Recombinant RhoA^wild-pEGFP-N1 and RhoA^S188A-pEGFP-N1 plasmids were constructed and transfected into primary hippocampal nerve cells (HNCs) to evaluate the neuroprotective mechanism of endothelial H₂S by using transwell co-culture system with endothelial cells from cystathionine-γ-lyase knockout (CSE^-/-) mice and 3-mercaptopyruvate sulfurtransferase knockout (3-MST^-/-) rats, respectively. We found that NaHS, exogenous H₂S donor, promoted RhoA phosphorylation at Ser188 in the presence of cGMP-dependent protein kinase 1 (PKG1) in vitro. Besides, both exogenous and endothelial H₂S facilitated the RhoA phosphorylation at Ser188 in HNCs, which induced the reduction of RhoA activity and membrane transposition, as well as ROCK₂ activity and expression. To further investigate the role of endothelial H₂S on RhoA phosphorylation, we detected H₂S release from ECs of CSE^+/+ and CSE^-/- mice, and 3-MST^+/+ and 3-MST^-/- rats, respectively, and found that H₂S produced by ECs in the culture medium is mainly catalyzed by CSE synthase. Moreover, we revealed that both endothelial H₂S, mainly catalyzed by CSE, and exogenous H₂S protected the HNCs against hypoxia-reoxygenation injury via phosphorylating RhoA at Ser188.

Exogenous hydrogen sulfide protects against hepatic ischemia/reperfusion injury by inhibiting endoplasmic reticulum stress and cell apoptosis

The aim of the present study was to explore the effect of exogenous hydrogen sulphide (H₂S) on endoplasmic reticulum (ER) stress (ERS) in a rat model of hepatic ischemia/reperfusion (I/R) injury. A total of 48 Sprague-Dawley rats were randomly divided into four groups (n=12/group) as follows: Sham, I/R, I/R preceded by NaHS (I/R-NaHS) and I/R preceded by L-C-propargylglycine (PAG), a H₂S inhibitor (I/R-PAG). With the exception of the sham group, the rats in the other groups were subjected to 30 min hepatic warm ischemia followed by reperfusion for 6 or 12 h. Hepatic function was evaluated by serum concentrations of alanine aminotransferase (ALT). Apoptosis of hepatic cells was assessed by TUNEL staining and measurement of caspase-12 expression. The expression levels of ERS-associated proteins and mRNAs of pancreatic ER eukaryotic translation initiation factor-2a kinase (PERK), activating transcription factor-6 (ATF6), glucose-regulated protein (GRP) 78, TNF-receptor-associated factor (TRAF)-2, C/EBP homologous protein (CHOP) and caspase-12 were also measured by western blotting and reverse transcription-quantitative PCR. The serum concentrations of ALT in the I/R and I/R-PAG groups were found to be significantly higher compared with those in the sham and I/R-NaHS groups after 6 h of reperfusion; in addition, the ALT level returned to normal in the I/R group, while it increased further in the I/R-PAG group after 12 h of reperfusion. A higher cell apoptosis rate was observed in the I/R and I/R-PAG groups and the highest cell apoptosis rate was observed in the I/R-PAG group; correspondingly, the expression of caspase-12 was increased in the I/R and I/R-PAG groups. H₂S appeared to significantly attenuate hepatic I/R-induced ERS response, as indicated by the decreased expression of ATF6, PERK, GRP78, TRAF2 and CHOP. Endogenous H₂S may serve a hepatoprotective function after I/R, and inhibition of endogenous H₂S results in aggravation of I/R damage. Exogenous H₂S was shown to inhibit ERS-related gene expression, leading to suppression of inflammatory reaction and improvement of I/R damage. Therefore, exogenous H₂S has therapeutic potential to alleviate hepatic I/R injury.

Development and Application of Activity-based Fluorescent Probes for High-Throughput Screening

High-throughput screening facilitates the rapid identification of novel hit compounds; however, it remains challenging to design effective high-throughput assays, partially due to the difficulty of achieving sensitivity in the assay techniques. Among the various analytical methods that are used, fluorescence-based assays dominate owing to their high sensitivity and ease of operation. Recent advances in activity-based sensing/imaging have further expanded the availability of fluorescent probes as monitors for high-throughput screening of result outputs. In this study, we have reviewed various activity-based fluorescent probes used in high-throughput screening assays, emphasizing their structure-related working mechanisms. Moreover, we have explored the possibility of the development of additional and better probes to boost hit identification and drug development against various targets.

A H2 S-Specific Ultrasensitive Fluorogenic Probe Reveals TMV-Induced H2 S Production to Limit Virus Replication

Understanding the role of H₂ S in host defense mechanisms against RNA viruses may provide opportunities for the development of antivirals to combat viral infections. Here, we have developed a green-emitting fluorogenic probe, which exhibits a large fluorescence response at 520 nm (>560-fold) when treated with 100 μM H₂ S for 1 h. It is highly selective for H₂ S over biothiols (>400-fold F/F₀ ) and has a detection limit of 12.9 nM. We demonstrate the application of the probe for endogenous H₂ S detection in vivo for the understanding of its roles in antiviral host defense. Such virus-induced H₂ S inhibits viral replication by reducing gene expression of RNA-dependent RNA polymerase (RdRp) and coat protein (CP). Additionally, a H₂ S donor GYY4137 showed significantly antiviral activity as ribavirin, a broad-spectrum drug against RNA viruses. Furtherly, we propose a possible molecular mechanism for the TMV-induced H₂ S biogenesis. This work provides a proof-of-principle in support of further studies identifying endogenous H₂ S and its donors as potential antivirals toward RNA viruses.

Hydrogen sulfide in longevity and pathologies: Inconsistency is malodorous

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

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague-Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO₂ and sO₂ and increases in pCO₂ (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.

Hydrogen Sulfide Oxidation by Sulfide Quinone Oxidoreductase

Hydrogen sulfide (H2 S) is an environmental toxin and a heritage of ancient microbial metabolism that has stimulated new interest following its discovery as a neuromodulator. While many physiological responses have been attributed to low H2 S levels, higher levels inhibit complex IV in the electron transport chain. To prevent respiratory poisoning, a dedicated set of enzymes that make up the mitochondrial sulfide oxidation pathway exists to clear H2 S. The committed step in this pathway is catalyzed by sulfide quinone oxidoreductase (SQOR), which couples sulfide oxidation to coenzyme Q10 reduction in the electron transport chain. The SQOR reaction prevents H2 S accumulation and generates highly reactive persulfide species as products; these can be further oxidized or can modify cysteine residues in proteins by persulfidation. Here, we review the kinetic and structural characteristics of human SQOR, and how its unconventional redox cofactor configuration and substrate promiscuity lead to sulfide clearance and potentially expand the signaling potential of H2 S. This dual role of SQOR makes it a promising target for H2 S-based therapeutics.

Hydrogen Sulfide-Clues from Evolution and Implication for Neonatal Respiratory Diseases

Reactive oxygen species (ROS) have been the focus of redox research in the realm of oxidative neonatal respiratory diseases such as bronchopulmonary dysplasia (BPD). Over the years, nitric oxide (NO) and carbon monoxide (CO) have been identified as important gaseous signaling molecules involved in modulating the redox homeostasis in the developing lung. While animal data targeting aspects of these redox pathways have been promising in treating and/or preventing experimental models of neonatal lung disease, none are particularly effective in human neonatal clinical trials. In recent years, hydrogen sulfide (H2S) has emerged as a novel gasotransmitter involved in a magnitude of cellular signaling pathways and functions. The importance of H2S signaling may lie in the fact that early life-forms evolved in a nearly anoxic, sulfur-rich environment and were dependent on H2S for energy. Recent studies have demonstrated an important role of H2S and its synthesizing enzymes in lung development, which normally takes place in a relatively hypoxic intrauterine environment. In this review, we look at clues from evolution and explore the important role that the H2S signaling pathway may play in oxidative neonatal respiratory diseases and discuss future opportunities to explore this phenomenon in the context of neonatal chronic lung disease.

Decreased Plasma Hydrogen Sulfide Level Is Associated With the Severity of Depression in Patients With Depressive Disorder

Accumulating evidence has suggested a dysfunction of synaptic plasticity in the pathophysiology of depression. Hydrogen sulfide (H₂S), an endogenous gasotransmitter that regulates synaptic plasticity, has been demonstrated to contribute to depressive-like behaviors in rodents. The current study investigated the relationship between plasma H₂S levels and the depressive symptoms in patients with depression. Forty-seven depressed patients and 51 healthy individuals were recruited in this study. The 17-item Hamilton Depression Rating Scale (HAMD-17) was used to evaluate depressive symptoms for all subjects and the reversed-phase high-performance liquid chromatography (RP-HPLC) was used to measure plasmaH₂S levels. We found that plasma H₂S levels were significantly lower in patients with depression relative to healthy individuals (P < 0.001). Compared with healthy controls (1.02 ± 0.34 μmol/L), the plasma H₂S level significantly decreased in patients with mild depression (0.84 ± 0.28 μmol/L), with moderate depression (0.62 ± 0.21μmol/L), and with severe depression (0.38 ± 0.18 μmol/L). Correlation analysis revealed that plasma H₂S levels were significantly negatively correlated with the HAMD-17 scores in patients (r = -0.484, P = 0.001). Multivariate linear regression analysis showed that plasma H₂S was an independent contributor to the HAMD-17 score in patients (B = -0.360, t = -2.550, P = 0.015). Collectively, these results suggest that decreased H₂S is involved in the pathophysiology of depression, and plasma H₂S might be a potential indicator for depression severity.

The Capacity to Produce Hydrogen Sulfide (H2S) via Cysteine Degradation Is Ubiquitous in the Human Gut Microbiome

As one of the three mammalian gasotransmitters, hydrogen sulfide (H₂S) plays a major role in maintaining physiological homeostasis. Endogenously produced H₂S plays numerous beneficial roles including mediating vasodilation and conferring neuroprotection. Due to its high membrane permeability, exogenously produced H₂S originating from the gut microbiota can also influence human physiology and is implicated in reducing intestinal mucosal integrity and potentiating genotoxicity and is therefore a potential target for therapeutic interventions. Gut microbial H₂S production is often attributed to dissimilatory sulfate reducers such as Desulfovibrio and Bilophila species. However, an alternative source for H₂S production, cysteine degradation, is present in some gut microbes, but the genes responsible for cysteine degradation have not been systematically annotated in all known gut microbes. We classify mechanisms of cysteine degradation into primary, secondary, and erroneous levels of H₂S production and perform a comprehensive search for primary, secondary, and erroneous cysteine-degrading enzymes in 4,644 non-redundant bacterial genomes from the Unified Human Gastrointestinal Genome (UHGG) catalog. Of the 4,644 genomes we have putatively identified 2,046 primary, 1,951 secondary, and 5 erroneous cysteine-degrading species. We identified the presence of at least one putative cysteine-degrading bacteria in metagenomic data of 100% of 6,623 healthy subjects and the expression of cysteine-degrading genes in metatranscriptomic data of 100% of 736 samples taken from 318 individuals. Additionally, putative cysteine-degrading bacteria are more abundant than sulfate-reducing bacteria across healthy controls, IBD patients and CRC patients (p < 2.2e-16, Wilcoxon rank sum test). Although we have linked many taxa with the potential for cysteine degradation, experimental validation is required to establish the H₂S production potential of the gut microbiome. Overall, this study improves our understanding of the capacity for H₂S production by the human gut microbiome and may help to inform interventions to therapeutically modulate gut microbial H₂S production.

Emerging analytical tools for the detection of the third gasotransmitter H2S, a comprehensive review

BACKGROUND

Hydrogen sulfide (H2S) is currently considered among the endogenously produced gaseous molecules that exert various signaling effects in mammalian species. It is the third physiological gasotransmitter discovered so far after NO and CO. H2S was originally ranked among the toxic gases at elevated levels to humans. Currently, it is well-known that, in the cardiovascular system, H2S exerts several cardioprotective effects including vasodilation, antioxidant regulation, inhibition of inflammation, and activation of anti-apoptosis. With an increasing interest in monitoring H2S, the development of analysis methods should now follow.

AIM OF REVIEW

This review stages special emphasis on the several analytical technologies used for its determination including spectroscopic, chromatographic, and electrochemical methods. Advantages and limitations with regards to the application of each technique are highlighted with special emphasis on its employment for H2S in vivo measurement i.e., biofluids, tissues.

KEY SCIENTIFIC CONCEPTS AND IMPORTANT FINDINGS OF REVIEW

Fluorescence methods applied for H2S measurement offer an attractive non-invasive and promising approach in addition to its selectivity, however they cannot be considered as H2S-specific probes. On the other hand, colorimetric assays are among the most common methods used for in vitro H2S detection, albeit their employment in vivo H2S measurement has not yet been possible . Separation techniques such as gas or liquid chromatography offer higher selectivity compared to direct spectrophotometric or fluorescence methods especially for suitable for endpoint H2S measurements i.e. plasma or tissue samples. Despite all the developed analytical procedures used for H2S determination, the need for highly selective, much work should be devoted to resolve all the pitfalls of the current methods.

H2S promotes developmental brain angiogenesis via the NOS/NO pathway in zebrafish

Background

Hydrogen sulphide (H₂S) is considered as the third member of the gasotransmitter family, along with nitric oxide (NO) and carbon monoxide. H₂S has been reported to induce angiogenesis by promoting the growth, migration and tube-like structure formation of endothelial cells. Those studies were conducted in conditions of cell culture, mouse Matrigel plug assay model, rat wound healing model or rat hindlimb ischaemia model. Recent in vivo studies showed the physiological importance of H₂S in muscle angiogenesis. However, the importance of endogenous H₂S for brain angiogenesis during development remains unknown. We therefore aimed at determining the role of H₂S in brain vascular development.

Methods and results

Both knockdown and knockout of H₂S-producing enzymes, cystathionine β-synthase (cbs) and cystathionine γ-lyase (cth), using morpholino oligonucleotides and clustered regularly interspaced short palindromic repeats/Cas9-mediated mutation, impaired brain vascular development of larval zebrafish. Incubation with the slow-releasing H₂S donor GYY4137 alleviated the defects of brain vascular development in cbs and cth morphants. Quantitative analysis of the midbrain vascular network showed that H₂S enhances angiogenesis without affecting the topological structure of the brain vasculature. Mechanically, nitric oxide synthase 2a (nos2a) expression and NO production were decreased in both cbs and cth morphants. Overexpression of nos2a by coinjection of cbs or cth MO with full-length zebrafish nos2a mRNA alleviated the brain vascular developmental defects in cbs and cth morphants.

Conclusion

We conclude that H₂S promotes brain developmental angiogenesis via the NOS/NO pathway in zebrafish.

Bacterial metabolism-inspired molecules to modulate antibiotic efficacy

The decreasing antibiotic susceptibility of bacterial pathogens calls for novel antimicrobial therapies. Traditional screening pathways based on drug-target interaction have gradually reached the stage of diminishing returns. Thus, novel strategies are urgently needed in the fight against antibiotic-refractory bacteria, particularly for tolerant bacteria. Recently, evidence has accumulated demonstrating that microbial changes caused by bacterial metabolic processes significantly modulate antibiotic killing. A better understanding of these bacterial metabolic processes is indicating a need to screen novel metabolic modulators as potential antibiotic adjuvants. In this review, we describe the state of our current knowledge about how these bacterial metabolism-inspired molecules affect antibiotic efficacy, including potentiation and inhibition activity. In addition, the challenges faced and prospects for bringing them into clinic are also discussed. These examples may provide candidates or targets for the development of novel antibiotic adjuvants.

Fluorescent probe for detecting hydrogen sulfide based on disulfide nucleophilic substitution-addition

In view of the importance of hydrogen sulfide (H₂S) in the organism, a fast, noninvasive method for the detection of H₂S in situ is needed. Fluorescent probes based on disulfide-bond nucleophilic substitution-addition can selectively detect H₂S in vivo, which is very popular because it allows quick response for H₂S, thus it will be a useful tool for monitoring H₂S in the vivo. We developed a dicyanoisopentanone-based H₂S fluorescent probe (EW-H) that used a disulfide group as a self-destructive linker reaction site. Under the nucleophilic substitution of H₂S, the disulfide bond of EW-H was cleaved, and then nucleophilic addition took place intramolecularly to release the fluorophore (at 580 nm). The response to H₂S, EW-H had high sensitivity (86 nM of the detection limit), large Stokes shift (155 nm) and a fast response time. More importantly, the probe was also applied for bioimaging in HepG2 cells, indicating its potential applications in biological organism.

One-Step Assembly of Fluorescence-Based Cyanide Sensors from Inexpensive, Off-The-Shelf Materials

We report a simple and versatile approach to assemble sensitive and selective fluorescence “turn-on” sensors for cyanide by combining three off-the-shelf materials; namely fluorescent dye, 1-vinyl imidazole polymer, and cupric chloride. The cyanide-sensing species is a non-fluorescent fluorophore-polymer-Cu²⁺ complex; which forms as a result of the imidazole polymer’s ability to bind both fluorophore and fluorescence quencher (Cu²⁺). Cyanide removes Cu²⁺ from these complexes; thereby “turning-on” sensor fluorescence. These sensors are water-soluble and have a detection limit of ~2.5 μM (CN⁻) in water. Our ternary complex-based sensing approach also enables facile emission tuning; we demonstrate the convenient, synthesis-free preparation of blue and green-emitting sensors using distyrylbiphenyl and fluorescein fluorophores, respectively. Furthermore; these ternary complexes are easily immobilized using agarose to create cyanide-sensing hydrogels; which are then used in a simple; novel microdiffusion apparatus to achieve interference-free cyanide analysis of aqueous media. The present study provides an inexpensive approach for portable; interference-free cyanide detection.

Dismantling and Rebuilding the Trisulfide Cofactor Demonstrates Its Essential Role in Human Sulfide Quinone Oxidoreductase

Sulfide quinone oxidoreductase (SQOR) catalyzes the first step in sulfide clearance, coupling H₂S oxidation to coenzyme Q reduction. Recent structures of human SQOR revealed a sulfur atom bridging the SQOR active site cysteines in a trisulfide configuration. Here, we assessed the importance of this cofactor using kinetic, crystallographic, and computational modeling approaches. Cyanolysis of SQOR proceeds via formation of an intense charge transfer complex that subsequently decays to eliminate thiocyanate. We captured a disulfanyl-methanimido thioate intermediate in the SQOR crystal structure, revealing how cyanolysis leads to reversible loss of SQOR activity that is restored in the presence of sulfide. Computational modeling and MD simulations revealed an ∼10⁵-fold rate enhancement for nucleophilic addition of sulfide into the trisulfide versus a disulfide cofactor. The cysteine trisulfide in SQOR is thus critical for activity and provides a significant catalytic advantage over a cysteine disulfide.

Highly efficient H2S scavengers via thiolysis of positively-charged NBD amines

H2S is a well-known toxic gas and also a gaseous signaling molecule involved in many biological processes. Advanced chemical tools that can regulate H2S levels in vivo are useful for understanding H2S biology as well as its potential therapeutic effects. To this end, we have developed a series of 7-nitro-1,2,3-benzoxadiazole (NBD) amines as potential H2S scavengers. The kinetic studies of thiolysis reactions revealed that incorporation of positively-charged groups onto the NBD amines greatly increased the rate of the H2S-specific thiolysis reaction. We demonstrate that these reactions proceed effectively, with second order rate constants (k 2) of >116 M-1 s-1 at 37 °C for NBD-S8. Additionally, we demonstrate that NBD-S8 can effectively scavenge enzymatically-produced and endogenous H2S in live cells. Furthering the biological significance, we demonstrate NBD-S8 mediates scavenging of H2S in mice.

Engineering Metal-Organic Frameworks (MOFs) for Controlled Delivery of Physiological Gaseous Transmitters

Metal-organic frameworks (MOFs) comprising metal ions or clusters coordinated to organic ligands have become a class of emerging materials in the field of biomedical research due to their bespoke compositions, highly porous nanostructures, large surface areas, good biocompatibility, etc. So far, many MOFs have been developed for imaging and therapy purposes. The unique porous nanostructures render it possible to adsorb and store various substances, especially for gaseous molecules, which is rather challenging for other types of delivery vectors. In this review, we mainly focus on the recent development of MOFs for controlled release of three gaseous transmitters, namely, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S). Although these gaseous molecules have been known as air pollutants for a long time, much evidence has been uncovered regarding their important physiological functions as signaling molecules. These signaling molecules could be either physically absorbed onto or covalently linked to MOFs, allowing for the release of loaded signaling molecules in a spontaneous or controlled manner. We highlight the designing concept by selective examples and display their potential applications in many fields such as cancer therapy, wound healing, and anti-inflammation. We hope more effort could be devoted to this emerging fields to develop signaling molecule-releasing MOFs with practical applications.

Hydrogen Sulfide and Endoplasmic Reticulum Stress: A Potential Therapeutic Target for Central Nervous System Degeneration Diseases

There are three members of the endogenous gas transmitter family. The first two are nitric oxide and carbon monoxide, and the third newly added member is hydrogen sulfide (H₂S). They all have similar functions: relaxing blood vessels, smoothing muscles, and getting involved in the regulation of neuronal excitation, learning, and memory. The cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfur transferase acts together with cysteine aminotransferase (3-MST/CAT), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfur transferase with D-amino acid oxidase (3-MST/DAO) pathways are involved in the enzymatic production of H₂S. More and more researches focus on the role of H₂S in the central nervous system (CNS), and H₂S plays a significant function in neuroprotection processes, regulating the function of the nervous system as a signaling molecule in the CNS. Endoplasmic reticulum stress (ERS) and protein misfolding in its mechanism are related to neurodegenerative diseases. H₂S exhibits a wide variety of cytoprotective and physiological functions in the CNS degenerative diseases by regulating ERS. This review summarized on the neuroprotective effect of H₂S for ERS played in several CNS diseases including Alzheimer’s disease, Parkinson’s disease, and depression disorder, and discussed the corresponding possible signaling pathways or mechanisms as well.