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

Real-time detection of enzymatically formed hydrogen sulfide by pathogenic variants of cystathionine beta-synthase using hemoglobin I of Lucina pectinata as a biosensor

Classical homocystinuria is a rare disease caused by mutations in cystathionine β-synthase (CBS) gene (OMIM 613381). CBS catalyzes the first step of the transsulfuration pathway that converts homocysteine (Hcy) into cystathionine (Cysta) via a number of co-substrates and mechanisms. Formation of Cysta by condensation of Hcy and cysteine (Cys) produces a molar equivalent of hydrogen sulfide (H2S). H2S plays important roles in cognitive and vascular functions. Clinically, patients with CBS deficiency present with vascular, ocular, neurological and skeletal impairments. Biochemically, CBS deficiency manifests with elevated Hcy and reduced concentration of Cysta in plasma and urine. A number of pathogenic variants of human CBS have been characterized by their residual enzymatic activity, but very few studies have examined H2S production by pathogenic CBS variants, possibly due to technical hurdles in H2S detection and quantification. We describe a method for the real-time, continuous quantification of H2S formed by wild-type and pathogenic variants of human recombinant CBS, as well as by fibroblast extracts from healthy controls and patients diagnosed with CBS deficiency. The method takes advantage of the specificity and high affinity of hemoglobin I of the clam Lucina pectinata toward H2S and is based on UV-visible spectrophotometry. Comparison with the gold-standard, end-point H2S quantification method employing monobromobimane, as well as correlations with CBS enzymatic activity determined by LC-MS/MS showed agreement and correlation, and permitted the direct, time-resolved determination of H2S production rates by purified human recombinant CBS and by CBS present in fibroblast extracts. Rates of H2S production were highest for wild-type CBS, and lower for pathogenic variants. This method enables the examination of structural determinants of CBS that are important for H2S production and its possible relevance to the clinical outcome of patients.

Endogenous hydrogen sulfide accelerated trauma-induced heterotopic ossification through the Ca2+/ERK pathway-enhanced aberrant osteogenic activity

Unveiling of the mechanism involved in the occurrence and development of trauma-induced heterotopic ossification (tHO) is highly demanding due to current ineffective clinical treatment for it. Previous studies proposed that hydrogen sulfide (H2S) was vital for fate determination of stem cells, suggesting a potential role in the regulation of tHO development. In the current study, We found that expression of metabolic enzyme within sulfur conversion pathway was enhanced after tendon injury, leading to H2S accumulation within the tHO region. Increased production of endogenous H2S was shown to promote aberrant osteogenic activity of tendon-derived stem cells (TDSCs), which accelerated tHO formation. The inhibition of metabolic enzyme of H2S production or directly absorption of H2S could abolished osteogenic induction of TDSCs and the formation of tHO. Mechanistically, through RNA sequencing combined with rescue experiments, we demonstrated that activation of Ca2+/ERK pathway was the downstream molecular event of H2S-induced osteogenic commitment of TDSCs and tHO. For treatment strategy exploration, zine oxide nanoparticles (ZnO) as an effective H2S elimination material was validated to ideally halt the tHO formation in this study. Furthermore, in terms of chirality of nanoparticles, D-ZnO or L-ZnO nanoparticles showed superiority over R-ZnO nanoparticles in both clearing of H2S and inhibition of tHO. Our study not only revealed the mechanism of tHO through the endogenous gas signaling event from a new perspective, but also presented a applicable platform for elimination of the inordinate gas production, thus aiding the development of clinical treatment for tHO.

Biophysical characterization of hydrogen sulfide: A fundamental exploration in understanding significance in cell signaling

Hydrogen sulfide (H₂S) has emerged as a significant signaling molecule involved in various physiological processes, including vasodilation, neurotransmission, and cytoprotection. Its interactions with biomolecules are critical to understand its roles in health and disease. Recent advances in biophysical characterization techniques have shed light on the complex interactions of H₂S with proteins, nucleic acids, and lipids. Proteins are primary targets for H₂S, which can modify cysteine residues through S-sulfhydration, impacting protein function and signaling pathways. Advanced spectroscopic techniques, such as mass spectrometry and NMR, have enabled the identification of specific sulfhydrated sites and provided insights into the structural and functional consequences of these modifications. Nucleic acids also interact with H₂S, although this area is less explored compared to proteins. Recent studies have demonstrated that H₂S can induce modifications in nucleic acids, affecting gene expression and stability. Techniques like gel electrophoresis and fluorescence spectroscopy have been utilized to investigate these interactions, revealing that H₂S can protect DNA from oxidative damage and modulate RNA stability and function. Lipids, being integral components of cell membranes, interact with H₂S, influencing membrane fluidity and signaling. Biophysical techniques such as electron paramagnetic resonance (EPR) and fluorescence microscopy have elucidated the effects of H₂S on lipid membranes. These studies have shown that H₂S can alter lipid packing and dynamics, which may impact membrane-associated signaling pathways and cellular responses to stress. In the current work we have integrated this with key scientific explainations to provide a comprehensive review.

Linking homocysteine and ferroptosis in cardiovascular disease: insights and implications

Homocysteine (Hcy) is a metabolic intermediate product derived from methionine. Hyperhomocysteinemia is a condition associated with various diseases. Hcy is recognized as a risk factor for cardiovascular disease (CVD). Ferroptosis, a novel form of cell death, is primarily characterized by substantial iron accumulation and lipid peroxidation. Recent research indicates a close association between ferroptosis and the pathophysiological processes of tumors, neurological diseases, CVD, and other ailments. However, limited research has been conducted on the impact of Hcy on ferroptosis. Therefore, this paper aimed to investigate the potential roles and mechanisms of homocysteine and ferroptosis in the context of cardiovascular disease. By conducting comprehensive literature research and analysis, we aimed to summarize recent advancements in understanding the effects of homocysteine on ferroptosis in cardiovascular diseases. This research contributes to a profound understanding of this critical domain.

Role of the gut-muscle axis in mitochondrial function of ageing muscle under different exercise modes

The fundamental role of the gut microbiota through the gut-muscle axis in skeletal muscle ageing is increasingly recognised. Metabolites derived from the intestinal microbiota are essential in maintaining skeletal muscle function and metabolism. The energy produced by mitochondria and moderate levels of reactive oxygen species can contribute to this process. Metabolites can effectively target the mitochondria, slowing the progression of muscle ageing and potentially representing a marker of ageing-related skeletal muscle loss. Moreover, mitochondria can contribute to the immune response, gut microbiota biodiversity, and maintenance of the intestinal barrier function. However, the causal relationship between mitochondrial function and gut microbiota crosstalk remains poorly understood. In addition to elucidating the regulatory pathways of the gut-muscle axis during the ageing process, we focused on the potential role of the "exercise-gut-muscle axis", which represents a pathway under stimulation from different exercise modes to induce mitochondrial adaptations, skeletal muscle metabolism and maintain intestinal barrier function and biodiversity stability. Meanwhile, different exercise modes can induce mitochondrial adaptations and skeletal muscle metabolism and maintain intestinal barrier function and biodiversity. Resistance exercise may promote mitochondrial adaptation, increase the cross-sectional area of skeletal muscle and muscle hypertrophy, and promote muscle fibre and motor unit recruitment. Whereas endurance exercise promotes mitochondrial biogenesis, aerobic capacity, and energy utilisation, activating oxidative metabolism-related pathways to improve skeletal muscle metabolism and function. This review describes the effects of different exercise modes through the gut-muscle axis and how they act through mitochondria in ageing to define the current state of the field and issues requiring resolution.

Cell membrane-targeted surface enhanced Raman scattering nanoprobes for the monitoring of hydrogen sulfide secreted from living cells

Hydrogen sulfide (H2S), an important gas signal molecule, participates in intercellular signal transmission and plays a considerable role in physiology and pathology. However, in-situ monitoring of H2S level during the processes of material transport between cells remains considerably challenging. Herein, a cell membrane-targeted surface-enhanced Raman scattering (SERS) nanoprobe was designed to quantitatively detect H2S secreted from living cells. The nanoprobes were fabricated by assembling cholesterol-functionalized DNA strands and dithiobis(phenylazide) (DTBPA) molecules on core-shell gold nanostars embedded with 4-mercaptoacetonitrile (4-MBN) (AuNPs@4-MBN@Au). Thus, three functions including cell-membrane targeted via cholesterol, internal standard calibration, and responsiveness to H2S through reduction of azide group in DTBPA molecules were integrated into the nanoprobes. In addition, the nanoprobes can quickly respond to H2S within 90 s and sensitively, selectively, and reliably detect H2S with a limit of detection as low as 37 nM due to internal standard-assisted calibration and reaction specificity. Moreover, the nanoprobes can effectively target on cell membrane and realize SERS visualization of dynamic H2S released from HeLa cells. By employing the proposed approach, an intriguing phenomenon was observed: the other two major endogenous gas transmitters, carbon monoxide (CO) and nitric oxide (NO), exhibited opposite effect on H2S production in living cells stimulated by related gas release molecules. In particular, the introduction of CO inhibited the generation of H2S in HeLa cells, while NO promoted its output. Thus, the nanoprobes can provide a robust method for investigating H2S-related extracellular metabolism and intercellular signaling transmission.

A lipid droplet-targeting fluorescent probe for specific H2S imaging in biosamples and development of smartphone platform

Hydrogen sulfide (H2S), a significant gas signal molecule, is closely related to various physiological/pathological processes. The monitoring of H2S is crucial in understanding the occurrence and development of diseases such as cancers. Emerging evidence suggests that abnormal regulation of Lipid droplets (LDs) is associated with many human diseases. For example, cancer cells are characterized by the abnormal accumulation of LDs. Therefore, understanding the relationship between LDs and cancer is of great significance for developing therapies against cancer. To address this challenge, we designed and developed a LD-targeting and H2S-activated probe (BTDA-DNB) by engineering a 2,4-dinitrophenyl ether (DNBE) as the H2S reactive site. In the presence of H2S, a strongly fluorescent emitter, 3-(benzo[d]thiazol-2-yl)-N,N-diethyl-2-imino-2H-chromen-7-amine (BTDA) was obtained with the leaving of DNBE group. BTDA-DNB displayed favorable sensitivity, selectivity and functioning well at physiological pH. The probe features excellent LD-targeting specificity and low cellular toxicity. The practical applications of LD-targeting probe BTDA-DNB as H2S probe in living cells, cancer tissues and Arabidopsis seedling have been evaluated. The excellent imaging performance demonstrates a potential ability for cancer diagnosis. Benefitted from the excellent performance on visual recognition H2S, a robust smartphone-integrated platform for H2S analysis was also successfully established.

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

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

H2S Donors with Cytoprotective Effects in Models of MI/R Injury and Chemotherapy-Induced Cardiotoxicity

Hydrogen sulfide (H2S) is an endogenous signaling molecule that greatly influences several important (patho)physiological processes related to cardiovascular health and disease, including vasodilation, angiogenesis, inflammation, and cellular redox homeostasis. Consequently, H2S supplementation is an emerging area of interest, especially for the treatment of cardiovascular-related diseases. To fully unlock the medicinal properties of hydrogen sulfide, however, the development and refinement of H2S releasing compounds (or donors) are required to augment its bioavailability and to better mimic its natural enzymatic production. Categorizing donors by the biological stimulus that triggers their H2S release, this review highlights the fundamental chemistry and releasing mechanisms of a range of H2S donors that have exhibited promising protective effects in models of myocardial ischemia-reperfusion (MI/R) injury and cancer chemotherapy-induced cardiotoxicity, specifically. Thus, in addition to serving as important investigative tools that further advance our knowledge and understanding of H2S chemical biology, the compounds highlighted in this review have the potential to serve as vital therapeutic agents for the treatment (or prevention) of various cardiomyopathies.

Facile synthesis of non-modified yellow emission silicon quantum dots and their visualization of hydrogen sulfide in living cells and onion tissues

Yellow fluorescent silicon quantum dots (y-SiQDs) with 22.2% fluorescence quantum yield were synthesized by a simple hydrothermal method using 3-glycidoxypropyl triethoxysilane (GOTS) and m-aminophenol. The excitation wavelength is 550 nm with an emission wavelength of 574 nm, which effectively avoids the interference of biological autofluorescence. Notably, the synthesis approach does not require any post-modification and the y-SiQDs can be directly used for hydrogen sulfide (H₂S) quantification due to static quenching. It exhibits high sensitivity and excellent selectivity for H₂S with a 0.2-10 μM (R² = 0.9953) linear range and detection limit of 54 nM. y-SiQDs have excellent stability and biocompatibility and can be used for H₂S imaging in living cells and onion tissues.

Short Chain Fatty Acid Metabolism in Relation to Gut Microbiota and Genetic Variability

It is widely accepted that the gut microbiota plays a significant role in modulating inflammatory and immune responses of their host. In recent years, the host-microbiota interface has gained relevance in understanding the development of many non-communicable chronic conditions, including cardiovascular disease, cancer, autoimmunity and neurodegeneration. Importantly, dietary fibre (DF) and associated compounds digested by the microbiota and their resulting metabolites, especially short-chain fatty acids (SCFA), were significantly associated with health beneficial effects, such as via proposed anti-inflammatory mechanisms. However, SCFA metabolic pathways are not fully understood. Major steps include production of SCFA by microbiota, uptake in the colonic epithelium, first-pass effects at the liver, followed by biodistribution and metabolism at the host's cellular level. As dietary patterns do not affect all individuals equally, the host genetic makeup may play a role in the metabolic fate of these metabolites, in addition to other factors that might influence the microbiota, such as age, birth through caesarean, medication intake, alcohol and tobacco consumption, pathogen exposure and physical activity. In this article, we review the metabolic pathways of DF, from intake to the intracellular metabolism of fibre-derived products, and identify possible sources of inter-individual variability related to genetic variation. Such variability may be indicative of the phenotypic flexibility in response to diet, and may be predictive of long-term adaptations to dietary factors, including maladaptation and tissue damage, which may develop into disease in individuals with specific predispositions, thus allowing for a better prediction of potential health effects following personalized intervention with DF.

DR1-CSE/H2S pathway upregulates autophagy and inhibits H9C2 cells damage induced by high glucose

In the cardiovascular system, long-term high glucose (HG) can lead to cardiomyocyte damage. Hydrogen sulfide (H₂S) reduces cell autophagy in cardiomyocytes. Dopamine 1 receptors (DR1), a specific binding receptor for dopamine, which has a significant regulatory effect on cardiomyocytes. However, it is unclear whether DR1 inhibits HG-induced cardiomyocyte damage by regulating endogenous H₂S production and the level of cell autophagy. The present data indicated that the expression of DR1 and cystathionine-γ-lyase (CSE, a key enzyme for endogenous H₂S production) and H₂S content were significantly reduced in HG-induced cardiomyocytes, which was reversed by SKF38393 (an agonist of DR1). NaHS (an exogenous H₂S donor) only increased H₂S content and the expression of CSE with no effect on DR1 expression. HG reduced cell viability, the expression of Bcl-2 and Beclin1, the production of autophagosomes and LC3 II/I ratio and increased the cell apoptotic ratio, the expression of cleaved caspase-3, cleaved caspase-9, cytochrome c, P62, and p-mTOR/t-mTOR ratio. SKF38393 and NaHS reversed the effects of HG. PPG (an inhibitor of CSE) and 3MA (an inhibitor of autophagy) abolished the beneficial effect of SKF38393. In addition, AICAR (an agonist of AMPK) and Rapamycin (an inhibitor of mTOR) increased the production of autophagosomes but decreased the p-mTOR/t-mTOR ratio, which was similar to the effects of SKF38393 and 3MA. Our findings suggest that DR1 reduces the HG-induced cardiomyocyte damage via up-regulating the CSE/H₂S pathway, which increases cell autophagy by inhibiting the activation of mTOR.

Improvement of Hydrogen Sulfide Scavenging via the Addition of Monoethanolamine to Water-Based Drilling Fluids

The release of the lethal hydrogen sulfide (H₂S) gas during the drilling of sour subterranean formations is of huge health and safety concern. Additionally, the contact of this corrosive gas with handling equipment might result in severe damages and significant economic losses. Accordingly, effective in situ scavenging of H₂S while drilling is very crucial. Thus, we report herein the addition of monoethanolamine (MEA) to water-based mud with the objective of improving the H₂S-scavenging efficacy of the mud. The H₂S-scavenging capacity was evaluated for the MEA-containing mud and compared with the base mud and fluids containing the commercial scavengers, SourScav and triazine. Also, the key mud characteristics including rheology, filtration properties, alkalinity, and corrosion rate were investigated in the presence and the absence of MEA, and the obtained results were compared to those of SourScav and triazine. The obtained experimental results revealed that the addition of MEA to the base mud significantly improved the H₂S adsorption capacity of the base mud by 117%, compared to 50 and 74% with the SourScav and triazine. Additionally, the pH value of the MEA-containing mud complied with the practical recommendations for drilling in a sour environment. Moreover, the plastic viscosity was increased by 13% to 37 cP with the MEA-containing mud with an insignificant impact on the yield point. Furthermore, the MEA-containing mud showed a favorable zero corrosion rate, as was the case for SourScav and triazine muds. However, unlike SourScav and triazine, MEA did not substantially enhance the filtration performance. Nonetheless, the filtration characteristics of the MEA-containing mud were still better than the base mud and within the recommended practical range for water-based muds. Overall, the results presented in this study reveal that the addition of monoethanolamine to water-based muds improves the mud characteristics and, more importantly, provides a superior H₂S-scavenging performance relative to SourScav and triazine scavengers, suggesting the commercial relevance of MEA for drilling applications.

Hydrogen sulfide decreases photodynamic therapy outcome through the modulation of the cellular redox state

Photodynamic therapy (PDT) is a non-surgical treatment that has been approved for its human medical use in many cancers. PDT involves the interaction of a photosensitizer (PS) with light. The amino acid 5- aminolevulinic acid (ALA) can be used as a pro-PS, leading to the synthesis of Protoporphyrin IX. Hydrogen sulfide (H₂S) is an endogenously produced gas that belongs to the gasotransmitter family, which can diffuse through biological membranes and have relevant physiological effects such as cardiovascular functions, vasodilatation, inflammation, cell cycle and neuro-modulation. It was also proposed to have cytoprotective effects. We aimed to study the modulatory effects of H₂S on ALAPDT in the mammary adenocarcinoma cell line LM2. Exposure of the cells to NaHS (donor of H₂S) in concentrations up to 10 mM impaired the response to ALA-PDT in a dose-dependent manner. The addition of 3 doses of NaHS showed the highest effect. This decreased response to the photodynamic treatment was correlated to an increase in the GSH levels, catalase activity, a dose dependent reduction of PpIX and increased intracellular ALA, decreased levels of oxidized proteins and a decrease of PDT-induced ROS. NaHS also reduced the levels of singlet oxygen in an in vitro assay. H₂S also protected other cells of different origins against PDT mediated by ALA and other PSs. These results suggest that H₂S has a role in the modulation of the redox state of the cells, and thus impairs the response to ALA-PDT through multifactor pathways. These findings could contribute to developing new strategies to improve the effectiveness of PDT particularly mediated by ALA or other ROS-related treatments.

A Whiff of Sulfur: One Wind a Day Keeps the Doctor Away

Reactive Sulfur Species (RSS), such as allicin from garlic or sulforaphane from broccoli, are fre-quently associated with biological activities and possible health benefits in animals and humans. Among these Organic Sulfur Compounds (OSCs) found in many plants and fungi, the Volatile Sulfur Compounds (VSCs) feature prominently, not only because of their often-pungent smell, but also because they are able to access places which solids and solutions cannot reach that easily. Indeed, inorganic RSS such as hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) can be used to lit-erally fumigate entire rooms and areas. Similarly, metabolites of garlic, such as allyl methyl sulfide (AMS), are formed metabolically in humans in lower concentrations and reach the airways from inside the body as part of one’s breath. Curiously, H₂S is also formed in the gastrointestinal tract by gut bacteria, and the question of if and for which purpose this gas then crosses the barriers and enters the body is indeed a delicate matter for equally delicate studies. In any case, nature is surprisingly rich in such VSCs, as fruits (for instance, the infamous durian) demonstrate, and therefore these VSCs represent a promising group of compounds for further studies.

NIR Fluorescent Probe for In Situ Bioimaging of Endogenous H2S in Rice Roots under Al3+ and Flooding Stresses

Hydrogen sulfide (H₂S) is one of the typical reactive sulfur species, which exhibits an important role in regulating both physiological and pathological processes. Recent studies indicate that H₂S also serves as a key signaling molecule in a broad range of regulatory processes in plants. However, in situ imaging and detection of the levels of H₂S in plant tissues remains a challenge. In this work, a NIR fluorescent probe (HBTP-H₂S) was synthesized to achieve H₂S imaging in living plant tissues. HBTP-H₂S exhibited high sensitivity toward H₂S with a large Stokes shift (250 nm). HBTP-H₂S could be applied to HeLa cells to detect the fluctuation of endogenous H₂S levels in response to physiological stimulations. Importantly, HBTP-H₂S was utilized for direct H₂S imaging of rice roots and revealed the upregulation of H₂S signaling in response to aluminum ions and flooding stresses. Our work thus provides a new tool to investigate H₂S-involved signal interaction and protective resistance of crops under environmental stresses.

Potential role of hydrogen sulfide in central nervous system tumors: a narrative review

Central nervous system tumors are classified as diseases of special clinical significance with high disability and high mortality. In addition to cerebrovascular diseases and craniocerebral injuries, tumors are the most common diseases of the central nervous system. Hydrogen sulfide, the third endogenous gas signaling molecule discovered in humans besides nitric oxide and carbon monoxide, plays an important role in the pathophysiology of human diseases. It is reported that hydrogen sulfide not only exerts a wide range of biological effects, but also develops a certain relationship with tumor development and neovascularization. A variety of studies have shown that hydrogen sulfide acts as a vasodilator and angiogenetic factor to facilitate growth, proliferation, migration and invasion of cancer cells. In this review, the pathological mechanisms and the effect of hydrogen sulfide on the central nervous system tumors are introduced.

Fluorescein Based Fluorescence Sensors for the Selective Sensing of Various Analytes

Fluorescein molecules are extensively used to develop fluorescent probes for various analytes due to their excellent photophysical properties and the spirocyclic structure. The main structural modification of fluorescein occurs at the carboxyl group where different groups can be easily introduced to produce the spirolactam structure which is non-fluorescent. The spirolactam ring opening accounts for the fluorescence and the dual sensing of analytes using fluorescent sensors is still a topic of high interest. There is an increase in the number of dual sensors developed in the past five years and quite a good number of fluorescein derivatives were also reported based on reversible mechanisms. This review analyses environmentally and biologically important cations such as Cu2+, Hg2+, Fe3+, Pd2+, Zn2+, Cd2+, and Mg2+; anions (F-, OCl-) and small molecules (thiols, CO and H2S). Structural modifications, binding mechanisms, different strategies and a comparative study for selected cations, anions and molecules are outlined in the article.

Microbial sulfur metabolism and environmental implications

Sulfur as a macroelement plays an important role in biochemistry in both natural environments and engineering biosystems, which can be further linked to other important element cycles, e.g. carbon, nitrogen and iron. Consequently, the sulfur cycling primarily mediated by sulfur compounds oxidizing microorganisms and sulfur compounds reducing microorganisms has enormous environmental implications, particularly in wastewater treatment and pollution bioremediation. In this review, to connect the knowledge in microbial sulfur metabolism to environmental applications, we first comprehensively review recent advances in understanding microbial sulfur metabolisms at molecular-, cellular- and ecosystem-levels, together with their energetics. We then discuss the environmental implications to fight against soil and water pollution, with four foci: (1) acid mine drainage, (2) water blackening and odorization in urban rivers, (3) SANI® and DS-EBPR processes for sewage treatment, and (4) bioremediation of persistent organic pollutants. In addition, major challenges and further developments toward elucidation of microbial sulfur metabolisms and their environmental applications are identified and discussed.

Role of hydrogen sulfide in ventilatory responses to hypercapnia in the medullary raphe of adult rats

NEW FINDINGS

What is the central question of this study? There is evidence that H₂ S plays a role in the control of breathing: what are its actions on the ventilatory and thermoregulatory responses to hypercapnia via effects in the medullary raphe, a brainstem region that participates in the ventilatory adjustments to hypercapnia? What is the main finding and its importance? Hypercapnia increased the endogenous production of H₂ S in the medullary raphe. Inhibition of endogenous H₂ S attenuated the ventilatory response to hypercapnia in unanaesthetized rats, suggesting its excitatory action via the cystathionine β-synthase-H₂ S pathway in the medullary raphe.

ABSTRACT

Hydrogen sulfide (H₂ S) has been recently recognized as a gasotransmitter alongside carbon monoxide (CO) and nitric oxide (NO). H₂ S seems to modulate the ventilatory and thermoregulatory responses to hypoxia and hypercapnia. However, the action of the H₂ S in the medullary raphe (MR) on the ventilatory responses to hypercapnia remains to be elucidated. The present study aimed to assess the role of H₂ S in the MR (a brainstem region that contains CO₂ -sensitive cells and participates in the ventilatory adjustments to hypercapnia) in the ventilatory responses to hypercapnia in adult unanaesthetized Wistar rats. To do so, aminooxyacetic acid (AOA; a cystathionine β-synthase (CBS) enzyme inhibitor), propargylglycine (PAG; a cystathionine γ-lyase enzyme inhibitor) and sodium sulfide (Na₂ S; an H₂ S donor) were microinjected into the MR. Respiratory frequency (f_R ), tidal volume (V_T ), ventilation ( V ̇ E ), oxygen consumption ( V ̇ O 2 ) and body temperature (T_b ) were measured under normocapnic (room air) and hypercapnic (7% CO₂ ) conditions. H₂ S concentration within the MR was determined. Microinjection of the drugs did not affect f_R , V_T and V ̇ E during normocapnia when compared to the control group. However, the microinjection of AOA, but not PAG, attenuated f_R and V ̇ E during hypercapnia in comparison to the vehicle group, but had no effects on T_b . In addition, we observed an increase in the endogenous production of H₂ S in the MR during hypercapnia. Our findings indicate that endogenously produced H₂ S in the MR plays an excitatory role in the ventilatory response to hypercapnia, acting through the CBS-H₂ S pathway.

Biosynthesis, Quantification and Genetic Diseases of the Smallest Signaling Thiol Metabolite: Hydrogen Sulfide

Hydrogen sulfide (H2S) is a gasotransmitter and the smallest signaling thiol metabolite with important roles in human health. The turnover of H2S in humans is mainly governed by enzymes of sulfur amino acid metabolism and also by the microbiome. As is the case with other small signaling molecules, disease-promoting effects of H2S largely depend on its concentration and compartmentalization. Genetic defects that impair the biogenesis and catabolism of H2S have been described; however, a gap in knowledge remains concerning physiological steady-state concentrations of H2S and their direct clinical implications. The small size and considerable reactivity of H2S renders its quantification in biological samples an experimental challenge. A compilation of methods currently employed to quantify H2S in biological specimens is provided in this review. Substantial discrepancy exists in the concentrations of H2S determined by different techniques. Available methodologies permit end-point measurement of H2S concentration, yet no definitive protocol exists for the continuous, real-time measurement of H2S produced by its enzymatic sources. We present a summary of available animal models, monogenic diseases that impair H2S metabolism in humans including structure-function relationships of pathogenic mutations, and discuss possible approaches to overcome current limitations of study.

Maternal Garlic Oil Supplementation Prevents High-Fat Diet-Induced Hypertension in Adult Rat Offspring: Implications of H2S-Generating Pathway in the Gut and Kidneys

SCOPE

Perinatal high-fat (HF) diet induces hypertension in adult offspring. Garlic, a naturally dietary source of Hydrogen sulfide (H2 S) donor, has been shown benefits in hypertension. The article examines whether maternal garlic oil supplementation can prevent hypertension induced by HF diet and elucidate its protective effects.

METHODS AND RESULTS

Pregnant rats are given either a normal diet or HF diet. Rat dams are given garlic oil or vehicle daily by oral gavage at 100 mg kg-1 day-1 during pregnancy and lactation. Male offspring are sacrificed at 16 weeks of age. Garlic oil supplementation during pregnancy and lactation protected against hypertension induced by HF diet in adult male offspring. The beneficial effects of garlic oil are associated with increased renal mRNA expression and activity of H2 S-generating enzymes, increased NO bioavailability, increased plasma short chain fatty acid levels, and alterations of gut microbiota composition. Garlic oil supplementation increases abundance of genus Lactobacillus, but decreases genera Turicibacter and Staphylococcus.

CONCLUSION

The data reveals associations between H2 S-generating pathway in the gut and kidneys, NO system, gut microbiota, and microbiota-derived metabolites in hypertension induced by HF intake and provide insight to garlic oil as a hypertension reprogramming strategy for further translational research.

Association of sulfur content in erythrocytes with cardiovascular parameters and blood pressure

OBJECTIVE

The study aims at assessing the relationship between blood pressure, heart geometry parameters, and the erythrocyte content of sulfur, potassium, chlorine and phosphorus, in a group of patients with laboratory systolic and diastolic blood pressure (SBP, DBP) below 140 or 90 mm Hg, respectively, who were otherwise healthy and untreated.

METHODS

The study group consisted of 42 adults recruited in a primary care setting. The individuals were healthy, not undergoing any therapy and free from smoking. For each individual, data were obtained on: average 24-hour SBP and DBP, left ventricle geometry, complete blood count, lipids profile, fibrinogen, hs-CRP and the erythrocyte concentration of sulfur (S), potassium (K), chlorine (Cl) and phosphorus (P).

RESULTS

Multivariate regression analysis showed statistically significant relationships of diastolic posterior wall thickness (PWTd) and relative wall thickness (RWT) with the concentration ratio of sulfur and potassium (S/K) in erythrocytes: PWTd and RWT increase as the S/K ratio increases. Also, SBP was found to be positively correlated with the S/K ratio.

CONCLUSIONS

The increase in sulfur content in RBCs could be an indicator of the downregulation of nitric oxide (NO) erythrocyte bioavailability exerted by endogenously produced hydrogen sulfide (H2S), and, in consequence, a marker of the development of hypertension and/or adverse changes in heart geometry.

Hyperhomocysteinemia and Cardiovascular Disease: Is the Adenosinergic System the Missing Link?

The influence of hyperhomocysteinemia (HHCy) on cardiovascular disease (CVD) remains unclear. HHCy is associated with inflammation and atherosclerosis, and it is an independent risk factor for CVD, stroke and myocardial infarction. However, homocysteine (HCy)-lowering therapy does not affect the inflammatory state of CVD patients, and it has little influence on cardiovascular risk. The HCy degradation product hydrogen sulfide (H2S) is a cardioprotector. Previous research proposed a positive role of H2S in the cardiovascular system, and we discuss some recent data suggesting that HHCy worsens CVD by increasing the production of H2S, which decreases the expression of adenosine A2A receptors on the surface of immune and cardiovascular cells to cause inflammation and ischemia, respectively.

Advances in the Protective Mechanism of NO, H2S, and H2 in Myocardial Ischemic Injury

Myocardial ischemic injury is among the top 10 leading causes of death from cardiovascular diseases worldwide. Myocardial ischemia is caused mainly by coronary artery occlusion or obstruction. It usually occurs when the heart is insufficiently perfused, oxygen supply to the myocardium is reduced, and energy metabolism in the myocardium is abnormal. Pathologically, myocardial ischemic injury generates a large number of inflammatory cells, thus inducing a state of oxidative stress. This sharp reduction in the number of normal cells as a result of apoptosis leads to organ and tissue damage, which can be life-threatening. Therefore, effective methods for the treatment of myocardial ischemic injury and clarification of the underlying mechanisms are urgently required. Gaseous signaling molecules, such as NO, H₂S, H₂, and combined gas donors, have gradually become a focus of research. Gaseous signaling molecules have shown anti-apoptotic, anti-oxidative and anti-inflammatory effects as potential therapeutic agents for myocardial ischemic injury in a large number of studies. In this review, we summarize and discuss the mechanism underlying the protective effect of gaseous signaling molecules on myocardial ischemic injury.

Maternal N-Acetylcysteine Therapy Prevents Hypertension in Spontaneously Hypertensive Rat Offspring: Implications of Hydrogen Sulfide-Generating Pathway and Gut Microbiota

Hypertension can come from early life. N-acetylcysteine (NAC), a hydrogen sulfide (H₂S) precursor as well as an antioxidant, has antihypertensive effect. We investigated whether maternal NAC therapy can protect spontaneously hypertensive rats (SHR) male offspring against hypertension. The pregnant rats were assigned to four groups: SHRs without treatment; Wistar Kyoto (WKY) without treatment; SHR+NAC, SHRs received 1% NAC in drinking water throughout pregnancy and lactation; and, WKY+NAC, WKY rats received 1% NAC in drinking water during pregnancy and lactation. Male offspring (n = 8/group) were killed at 12 weeks of age. Maternal NAC therapy prevented the rise in systolic blood pressure (BP) in male SHR offspring at 12 weeks of age. Renal cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulphurtransferase (3MST) protein levels and H₂S-releasing activity were increased in the SHR+NAC offspring. Maternal NAC therapy increased fecal H₂S and thiosulfate levels in the SHR+NAC group. Additionally, maternal NAC therapy differentially shaped gut microbiota and caused a distinct enterotype in each group. The protective effect of maternal NAC therapy against hypertension in SHR offspring is related to increased phylum Actinobacteria and genera Bifidobacterium and Allobaculum, but decreased phylum Verrucomicrobia, genera Turicibacter, and Akkermansia. Several microbes were identified as microbial markers, including genera Bifidobacterium, Allobaculum, Holdemania, and Turicibacter. Our results indicated that antioxidant therapy by NAC in pregnant SHRs can prevent the developmental programming of hypertension in male adult offspring. Our findings highlight the interrelationships among H₂S-generating pathway in the kidneys and gut, gut microbiota, and hypertension. The implications of maternal NAC therapy elicited long-term protective effects on hypertension in later life that still await further clinical translation.

Hydrogen sulfide signaling in regulation of cell behaviors

Recent advances in the biomedical importance of H₂S have help us understand various cellular functions and pathophysiological processes from a new aspect. Specially, H₂S has been demonstrated to play multiple roles in regulating cell behaviors, including cell survival, cell differentiation, cell senescence, cell hypertrophy, cell atrophy, cell metaplasia, and cell death, etc. H₂S contributes to cell behavior changes via various mechanisms, such as histone modification, DNA methylation, non-coding RNA changes, DNA damage repair, transcription factor activity, and post-translational modification of proteins by S-sulfhydration, etc. In this review, we summarized the recent research progress on H₂S signaling in control of cell behaviors and discussed the ways of H₂S regulation of gene expressions. Given the key roles of H₂S in both health and diseases, a better understanding of the regulation of H₂S on cell behavior change and the underlying molecular mechanisms will help us to develop novel and more effective strategies for clinical therapy.

Cysteine as a Carbon Source, a Hot Spot in Cancer Cells Survival

Cancer cells undergo a metabolic rewiring in order to fulfill the energy and biomass requirements. Cysteine is a pivotal organic compound that contributes for cancer metabolic remodeling at three different levels: (1) in redox control, free or as a component of glutathione; (2) in ATP production, via hydrogen sulfide (H₂S) production, serving as a donor to electron transport chain (ETC), and (3) as a carbon source for biomass and energy production. In the present review, emphasis will be given to the role of cysteine as a carbon source, focusing on the metabolic reliance on cysteine, benefiting the metabolic fitness and survival of cancer cells. Therefore, the interplay between cysteine metabolism and other metabolic pathways, as well as the regulation of cysteine metabolism related enzymes and transporters, will be also addressed. Finally, the usefulness of cysteine metabolic route as a target in cancer treatment will be highlighted.

Microbiota and Malodor-Etiology and Management

Accumulating evidence indicates that microbiota plays a critical role in physiological processes in humans. However, it might also contribute to body malodor by producing numerous odorous molecules such as ammonia, volatile sulfur compounds or trimethylamine. Although malodor is commonly overlooked by physicians, it constitutes a major problem for many otherwise healthy people. Thus, this review aims to investigate most common causes of malodor and describe potential therapeutic options. We searched PUBMED and Google Scholar databases to identify the clinical and pre-clinical studies on bad body smell, malodor, halitosis and microbiota. Unpleasant smell might originate from the mouth, skin, urine or reproductive fluids and is usually caused by odorants that are produced by resident bacterial flora. The accumulation of odorous compounds might result from diet, specific composition of microbiota, as well as compromised function of the liver, intestines and kidneys. Evidence-based guidelines for management of body malodor are lacking and no universal treatment exists. However, the alleviation of the symptoms may be achieved by controlling the diet and physical elimination of bacteria and/or accumulated odorants.

Aminooxyacetic acid (AOAA) sensitizes colon cancer cells to oxaliplatin via exaggerating apoptosis induced by ROS

Background: As the third confirmed gaseous transmitter, the role of hydrogen sulfide (H₂S) in the pathogenesis of multiple types of cancer has been attracting increasing attention. Increased expression of cystathionine β-synthase (CBS) and H₂S in colon cancer tissue samples has been validated and tumor-derived H₂S, mainly produced by CBS, stimulates bioenergetics, cell proliferation, and angiogenesis in colon cancer. Recently, the therapeutic manipulation of H₂S has been proposed as a promising anticancer approach. However, the effect of aminooxyacetic acid (AOAA), which has been widely used as an inhibitor of CBS dependent synthesis of H₂S, on the chemotherapeutic effect of oxaliplatin (OXA) and the underlying mechanisms remain to be illustrated.

Methods: We examined the expression of CBS in human colorectal cancer specimens and matched normal mucosa by immunohistochemistry. The effect of AOAA on the sensitivity of colon cancer cells to OXA and the level of apoptosis induced by caspase cascade was investigated in both HCT116 and HT29 cell lines utilizing CCK-8 assays, flow cytometry analysis and western blot analysis. The endogenous levels of reactive oxygen species (ROS) were detected fluorescently by DCF-DA, and glutathione (GSH) levels were measured by a Total GSH Detection Kit. Tumor bearing xenograft mouse models and in vivo imaging systems were further used to investigate the effect of AOAA in vivo and immunohistochemistry (IHC) and TUNEL analysis were performed.

Results: In the current study, we confirmed CBS, the main target of AOAA, is overexpressed in human colorectal cancer by immunohistochemistry. The inhibitory effect of AOAA on the synthesis of H₂S was validated utilizing fluorescent probe and specific electrode. AOAA significantly reduced the IC50 values of OXA in both colon cancer cell lines. Co-incubation with AOAA elicited increased apoptosis induced by OXA, featured by increased activation of caspase cascade. Besides, AOAA further increased the levels of ROS induced by OXA and attenuated the synthesis of glutathione (GSH), which is a vital antioxidant. Besides, the results of in vivo imaging and following IHC and TUNEL analysis were in accordance with cellular experiments, indicating that AOAA sensitizes colon cancer cells to OXA via exaggerating intrinsic apoptosis.

Conclusion: The results suggested that CBS is overexpressed in colorectal cancer tissues and AOAA sensitizes colon cancer cells to OXA via exaggerating apoptosis both in vitro and in vivo. Decreasing the endogenous level of GSH and consequently impaired detoxification of ROS might be one of the mechanisms underlying the effect of AOAA.

Hydrogen sulfide modulates epithelial-mesenchymal transition and angiogenesis in non-small cell lung cancer via HIF-1α activation

Hydrogen sulfide (H₂S) has been frequently implicated in tumor progression. However, the exact regulation mechanism of H₂S in human non-small cell lung cancer (NSCLC) has not been fully elucidated. Here, analysis of NSCLC biopsies and adjacent non-tumor tissues revealed selectively high levels of endogenous H₂S-producing enzymes, cystathionine-beta-synthase (CBS), cystathionine-gamma-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (MPST). Similarly, quantitative real-time PCR (qRT-PCR) and western blot results showed that NSCLC cell lines (A549, 95D) expressed higher levels of CBS, CSE and MPST in mRNA and enzyme proteins, respectively. Moreover, NSCLC cell lines produced more H₂S than did the normal lung epithelial cell line BEAS-2B. H₂S was further detected to induce NSCLC migration and invasion, as well as the epithelial mesenchymal transition (EMT) process. Small interfering RNA (siRNA) silencing of CBS or CSE activity reduced proliferation and metastasis potential of tumor cells. In addition, H₂S modulated hypoxia-inducible factor-1α (HIF-1α) to stimulate vascular endothelial growth factor (VEGF) expression, which contributes to tumor angiogenesis. Treatment of nude mice with pharmacological inhibition of CBS or CSE activity decreased xenograft growth and suppressed angiogenesis. Collectively, these results indicate H₂S plays an important part in NSCLC growth and angiogenesis by HIF-1α activation, which potentially provide new insight in therapeutic strategies.

The Effect of Hydrogen Sulfide on Different Parameters of Human Plasma in the Presence or Absence of Exogenous Reactive Oxygen Species

The main aim of the study is to examine the effect of sodium hydrosulfide (NaHS), an H₂S donor, on the oxidative stress in human plasma in vitro. It also examined the effects of very high concentrations of exogenous hydrogen sulfide on the hemostatic parameters (coagulation and fibrinolytic activity) of human plasma. Plasma was incubated for 5-30 min with different concentrations of NaHS from 0.01 to 10 mM. Following this, lipid peroxidation was measured as a thiobarbituric acid reactive substance (TBARS) concentration and the oxidation of amino acid residues in proteins was measured by determining the amounts of thiol groups and carbonyl groups. Hydrogen peroxide (H₂O₂) and the hydroxyl radical generating oxidation system (Fe/H₂O₂) were used as oxidative stress inducers. Hemostatic factors, such as the maximum velocity of clot formation, fibrin lysis half-time, the activated partial thromboplastin time (APTT), thrombin time (TT), and international normalized ratio (INR), were estimated. Changes in lipid peroxidation, carbonyl group formation, and thiol group oxidation were detected at high concentrations of H₂S (0.1-10 mM), and these results indicate that NaHS (as the precursor of H₂S) may have pro-oxidative effects in human plasma in vitro. Moreover, considering the data presented in this study, we suggest that the oxidative stress stimulated by NaHS (at high concentrations: 1-10 mM) is not involved in changes of the hemostatic activity of plasma.

Imbalance of Homocysteine and H2S: Significance, Mechanisms, and Therapeutic Promise in Vascular Injury

While the role of hyperhomocysteinemia in cardiovascular pathogenesis continuously draws attention, deficiency of hydrogen sulfide (H₂S) has been growingly implicated in cardiovascular diseases. Generation of H₂S is closely associated with the metabolism of homocysteine via key enzymes such as cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The level of homocysteine and H₂S is regulated by each other. Metabolic switch in the activity of CBS and CSE may occur with a resultant operating preference change of these enzymes in homocysteine and H₂S metabolism. This paper presented an overview regarding (1) linkage between the metabolism of homocysteine and H₂S, (2) mutual regulation of homocysteine and H₂S, (3) imbalance of homocysteine and H₂S in cardiovascular disorders, (4) mechanisms underlying the protective effect of H₂S against homocysteine-induced vascular injury, and (5) the current status of homocysteine-lowering and H₂S-based therapies for cardiovascular disease. The metabolic imbalance of homocysteine and H₂S renders H₂S/homocysteine ratio a potentially reliable biomarker for cardiovascular disease and development of drugs or interventions targeting the interplay between homocysteine and H₂S to maintain the endogenous balance of these two molecules may hold an even bigger promise for management of vascular disorders than targeting homocysteine or H₂S alone.

Estrogen Receptor-Related DNA and Histone Methylation May Be Involved in the Transgenerational Disruption in Spermatogenesis by Selective Toxic Chemicals

Air pollution is a global threat to human health especially spermatogenesis. Animal and epidemiological studies suggest that epigenetic factors can transmit the pathologies transgenerationally. Paternal epigenetic effects can greatly impact offspring health. In this study and together with our previous report, we found that H₂S donor Na₂S and/or NH₃ donor NH₄Cl diminished mouse fertility, decreased spermatozoa concentration and motility, and impaired spermatogenesis in three consequent generations (F0, F1, and F2). In the current study, we found that DNA methylation, histone methylation, and estrogen receptor alpha (ERα) were impaired by NH₄Cl and/or Na₂S in F0, F1, and F2 mouse testes. Moreover, NH₄Cl and/or Na₂S might act as environmental endocrine-disrupting chemicals to decrease estrogen and testosterone in mouse blood. It has been reported that ERα signaling is intertwined together with DNA methylation and histone methylation, which plays very important roles in spermatogenesis. These data together indicate that the transgenerational disruption in spermatogenesis by NH₄Cl and/or Na₂S may be through ERα-related DNA methylation and histone methylation pathways. Therefore, we strongly recommend that greater attention should be paid to NH₃ and/or H₂S contamination to minimize their impact on human health especially spermatogenesis.

Hydrogen Sulfide Attenuates Hydrogen Peroxide-Induced Injury in Human Lung Epithelial A549 Cells

Lung tissues are frequently exposed to a hyperoxia environment, which leads to oxidative stress injuries. Hydrogen sulfide (H₂S) is widely implicated in physiological and pathological processes and its antioxidant effect has attracted much attention. Therefore, in this study, we used hydrogen peroxide (H₂O₂) as an oxidative damage model to investigate the protective mechanism of H₂S in lung injury. Cell death induced by H₂O₂ treatment could be significantly attenuated by the pre-treatment of H₂S, resulting in a decrease in the Bax/Bcl-2 ratio and the inhibition of caspase-3 activity in human lung epithelial cell line A549 cells. Additionally, the results showed that H₂S decreased reactive oxygen species (ROS), as well as neutralized the damaging effects of H₂O₂ in mitochondria energy-producing and cell metabolism. Pre-treatment of H₂S also decreased H₂O₂-induced suppression of endogenous H₂S production enzymes, cystathionine-beta-synthase (CBS), cystathionine-gamma-lyase (CSE), and 3-mercapto-pyruvate sulfurtransferase (MPST). Furthermore, the administration of H₂S attenuated [Ca²⁺] overload and endoplasmic reticulum (ER) stress through the mitogen-activated protein kinase (MAPK) signaling pathway. Therefore, H₂S might be a potential therapeutic agent for reducing ROS and ER stress-associated apoptosis against H₂O₂-induced lung injury.

Gas Therapy: An Emerging “Green” Strategy for Anticancer Therapeutics

As an emerging area, gas therapy has attracted more and more attention in treating many diseases including cancer. The fabrication of stimuli‐responsive delivery systems with on‐demand release behavior is very promising for precision gas therapy, which can obtain optimal therapeutic performance without gas poisoning risks. In this review, the authors introduce the recent progress in the preparation of different kinds of gas carriers for efficient delivery of gaseous molecules (NO, H2S, CO, O2). Particularly, in order to achieve targeted accumulation of gaseous molecules in tumor tissues, gaseous molecules–integrated nanoparticles were constructed. Most importantly, by combination of gas therapy with other therapeutic modalities such as chemotherapy, photodynamic therapy (PDT), and radiotherapy, various multifunctional nanocarriers have been designed for synergistic cancer therapy. Especially, the recent developments of multifunctional gas‐carrying nanocarriers for synergistic cancer therapy are discussed in detail.

Decrease in male mouse fertility by hydrogen sulfide and/or ammonia can Be inheritable

Numerous epidemiological studies suggest that air pollutants cause a decline in the quality of human spermatozoa and thus a reduction in fertility. However, the exact cause of infertility remains unknown. Air pollution gases, such as NH₃ and H₂S are either free or bound to airborne particular materials (PM) and are abundant and reactive. The aim of this current investigation was to explore the impacts of NH₃ and/or H₂S on male fertility and the underlying mechanisms. Male mouse exposed to H₂S and/or NH₃ and after two generations were used to evaluate the impacts on fertility. The fertility, and spermatozoa quality parameters and proteins involved in spermatogenesis were investigated. Our current investigation demonstrates: i) H₂S and/or NH₃ decrease male fertility by 20-30%, reduce the spermatozoa concentration about 20-40%, decrease 10-20%, increase around 30%; ii) the reduction in male fertility by H₂S and/or NH₃ can be inheritable; iii) H₂S and/or NH₃ can diminish male fertility through the disruption of spermatogenesis without affecting other body parameters such as body weight and organ index. One component of air pollutants, for example NH₃, does not have a severe impact; however, two or more pollutants such as H₂S and NH₃ combined can cause serious health problems, especially with regard to male fertility. We suggest that greater attention should be paid to these air pollutants to improve human health and fertility.

Hydrogen sulfide is expressed in the human and the rat cultured nucleus pulposus cells and suppresses apoptosis induced by hypoxia

Apoptosis plays pivotal role in the pathogenesis of degenerative disc diseases, which is the primary contributor to low back pain. Although the role of hydrogen sulfide (H₂S) in cell apoptosis is well appreciated, the effects and mechanism that H₂S regulates the program death of intervertebral disc cell are not yet elucidated. In this study, we utilized the nucleus pulposus (NP) from patients with lumbar disc herniation to investigate the relationship between endogenous H₂S and NP cells apoptosis in human. Furthermore, we analyzed primary rat NP cells to study the effects of exogenous H₂S on hypoxia induced cell apoptosis. Human NP samples were obtained from patients with lumbar disc herniation and were divided into uncontained and contained herniation groups. Using immunohistochemistry staining and sulphur-sensitive electrode, we detected the expression of cystathionine-β-synthase (CBS) and cystathionine γ-lyase (CSE), as well as the production of endogenous H₂S in human NP. Tunel staining showed increased apoptosis in NP from herniated disc; and there was significant correlation between H₂S generation and apoptosis in human NP. CoCl₂ was then used to induce hypoxia in cultured primary rat NP cells. Annexin V staining indicated that exogenous NaHS attenuated hypoxia induced apoptosis in rat NP cells. Furthermore, hypoxia significantly increased the levels of multiple apoptosis associated proteins (Fas, Cytochromes C, Caspase 9 and cleaved-Caspase-3) in cells, which were eliminated by NaHS.

Our study demonstrates the presence of endogenous H₂S in human intervertebral disc; and the endogenous H₂S generation rate is associated with NP apoptosis in herniated disc. In vitro study showes exogenous H₂S donor attenuates hypoxia induced apoptosis in primary rat NP cells. Thus, our work provides insights that H₂S may have beneficial effects in treating degenerative disc diseases.

Reactive Precipitation of Anhydrous Alkali Sulfide Nanocrystals with Concomitant Abatement of Hydrogen Sulfide and Cogeneration of Hydrogen

Anhydrous alkali sulfide (M₂ S, M=Li or Na) nanocrystals (NCs) are important materials central to the development of next generation cathodes and solid-state electrolytes for advanced batteries, but not commercially available at present. This work reports an innovative method to directly synthesize M₂ S NCs through alcohol-mediated reactions between alkali metals and hydrogen sulfide (H₂ S). In the first step, the alkali metal is complexed with alcohol in solution, forming metal alkoxide (ROM) and releasing hydrogen (H₂ ). Next, H₂ S is bubbled through the ROM solution, where both chemicals are completely consumed to produce phase-pure M₂ S NC precipitates and regenerate alcohol that can be recycled. The M₂ S NCs morphology may be tuned through the choice of the alcohol and solvent. Both synthetic steps are thermodynamically favorable (ΔG_m^o <-100 kJ mol^-1 ), proceeding rapidly to completion at ambient temperature with almost 100 % atom efficiency. The net result, H₂ S+2 m→M₂ S+H₂ , makes good use of a hazardous chemical (H₂ S) and delivers two value-added products that naturally phase separate for easy recovery. This scalable approach provides an energy-efficient and environmentally benign solution to the production of nanostructured materials required in emerging battery technologies.

Anti-inflammatory effects of H2S during acute bacterial infection: a review

Hydrogen sulfide (H₂S), previously only considered a toxic environmental air pollutant, is now increasingly recognized as an important signaling molecule able to modulate several cellular pathways in many human tissues. As demonstrated in recent studies, H₂S is produced endogenously in response to different cellular stimuli and plays different roles in controlling a number of physiological responses. The precise role of H₂S in inflammation is still largely unknown. In particular, the role of H₂S in the regulation of the inflammatory response in acute and chronic infections is being actively investigated because of its potential therapeutic use. To study the effect of H₂S as an anti-inflammatory mediator during bacterial infections, we developed an ex vivo model of primary cells and cell lines infected with Mycoplasma. Our data demonstrate a dichotomic effect of H₂S on the NF-kB and Nrf-2 molecular pathways, which were inhibited and stimulated, respectively.

Hydrogen Sulfide and/or Ammonia Reduces Spermatozoa Motility through AMPK/AKT Related Pathways

A number of emerging studies suggest that air pollutants such as hydrogen sulfide (H₂S) and ammonia (NH₃) may cause a decline in spermatozoa motility. The impact and underlying mechanisms are currently unknown. Boar spermatozoa (in vitro) and peripubertal male mice (in vivo) were exposed to H₂S and/or NH₃ to evaluate the impact on spermatozoa motility. Na₂S and/or NH₄Cl reduced the motility of boar spermatozoa in vitro. Na₂S and/or NH₄Cl disrupted multiple signaling pathways including decreasing Na⁺/K⁺ ATPase activity and protein kinase B (AKT) levels, activating Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and phosphatase and tensin homolog deleted on chromosome ten (PTEN), and increasing reactive oxygen species (ROS) to diminish boar spermatozoa motility. The increase in ROS might have activated PTEN, which in turn diminished AKT activation. The ATP deficiency (indicated by reduction in Na⁺/K⁺ ATPase activity), transforming growth factor (TGF_β) activated kinase-1 (TAK1) activation, and AKT deactivation stimulated AMPK, which caused a decline in boar spermatozoa motility. Simultaneously, the deactivation of AKT might play some role in the reduction of boar spermatozoa motility. Furthermore, Na₂S and/or NH₄Cl declined the motility of mouse spermatozoa without affecting mouse body weight gain in vivo. Findings of the present study suggest that H₂S and/or NH₃ are adversely associated with spermatozoa motility.

Inhibition of hydrogen sulfide biosynthesis sensitizes lung adenocarcinoma to chemotherapeutic drugs by inhibiting mitochondrial DNA repair and suppressing cellular bioenergetics

Therapeutic manipulation of the gasotransmitter hydrogen sulfide (H₂S) has recently been proposed as a novel targeted anticancer approach. Here we show that human lung adenocarcinoma tissue expresses high levels of hydrogen sulfide (H₂S) producing enzymes, namely, cystathionine beta-synthase (CBS), cystathionine gamma lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST), in comparison to adjacent lung tissue. In cultured lung adenocarcinoma but not in normal lung epithelial cells elevated H₂S stimulates mitochondrial DNA repair through sulfhydration of EXOG, which, in turn, promotes mitochondrial DNA repair complex assembly, thereby enhancing mitochondrial DNA repair capacity. In addition, inhibition of H₂S-producing enzymes suppresses critical bioenergetics parameters in lung adenocarcinoma cells. Together, inhibition of H₂S-producing enzymes sensitize lung adenocarcinoma cells to chemotherapeutic agents via induction of mitochondrial dysfunction as shown in in vitro and in vivo models, suggesting a novel mechanism to overcome tumor chemoresistance.

Sulfmyoglobin Conformational Change: A Role in the Decrease of Oxy-Myoglobin Functionality

This work is focused at understanding the interaction of H2S with Myoglobin (Mb), in particular the Sulfmyoglobin (SMb) product, whose physiological role is controversial and not well understood. The scattering curves, Guinier, Kratky, Porod and P(r) plots were analyzed for oxy-Mb and oxy-Hemoglobin I (oxyHbI) in the absence and presence of H2S, using Small and Wide Angle X-ray Scattering (SAXS/WAXS) technique. Three dimensional models were also generated from the SAXS/WAXS data. The results show that SMb formation, produced by oxyMb and H2S interaction, induces a change in the protein conformation where its envelope has a very small cleft and the protein is more flexible, less rigid and compact. Based on the direct relationship between Mb's structural conformation and its functionality, we suggest that the conformational change observed upon SMb formation plays a contribution to the protein decrease in O2 affinity and, therefore, on its functionality.

Medical Functions of Hydrogen Sulfide

Hydrogen sulfide (H(2)S) is a gasomediator synthesized from L- and D-cysteine in various tissues. It is involved in a number of physiological and pathological processes. H(2)S exhibits antiatherosclerotic, vasodilator, and proangiogenic properties, and protects the kidney and heart from damage following ischemia/reperfusion injury. H(2)S donors may be natural or synthetic, and may be used for the safe treatment of a wide range of diseases. This review article summarizes the current state of knowledge of the therapeutic function of H(2)S.

Hydrogen Sulfide Signaling Axis as a Target for Prostate Cancer Therapeutics

Hydrogen sulfide (H₂S) was originally considered toxic at elevated levels; however just in the past decade H₂S has been proposed to be an important gasotransmitter with various physiological and pathophysiological roles in the body. H₂S can be generated endogenously from L-cysteine by multiple enzymes, including cystathionine gamma-lyase, cystathionine beta-synthase, and 3-mercaptopyruvate sulfurtransferase in combination with cysteine aminotransferase. Prostate cancer is a major health concern and no effective treatment for prostate cancers is available. H₂S has been shown to inhibit cell survival of androgen-independent, androgen-dependent, and antiandrogen-resistant prostate cancer cells through different mechanisms. Various H₂S-releasing compounds, including sulfide salts, diallyl disulfide, diallyl trisulfide, sulforaphane, and other polysulfides, also have been shown to inhibit prostate cancer growth and metastasis. The expression of H₂S-producing enzyme was reduced in both human prostate cancer tissues and prostate cancer cells. Androgen receptor (AR) signaling is indispensable for the development of castration resistant prostate cancer, and H₂S was shown to inhibit AR transactivation and contributes to antiandrogen-resistant status. In this review, we summarized the current knowledge of H₂S signaling in prostate cancer and described the molecular alterations, which may bring this gasotransmitter into the clinic in the near future for developing novel pharmacological and therapeutic interventions for prostate cancer.

L-Cysteine metabolism and its nutritional implications

L-Cysteine is a nutritionally semiessential amino acid and is present mainly in the form of L-cystine in the extracellular space. With the help of a transport system, extracellular L-cystine crosses the plasma membrane and is reduced to L-cysteine within cells by thioredoxin and reduced glutathione (GSH). Intracellular L-cysteine plays an important role in cellular homeostasis as a precursor for protein synthesis, and for production of GSH, hydrogen sulfide (H(2)S), and taurine. L-Cysteine-dependent synthesis of GSH has been investigated in many pathological conditions, while the pathway for L-cysteine metabolism to form H(2)S has received little attention with regard to prevention and treatment of disease in humans. The main objective of this review is to highlight the metabolic pathways of L-cysteine catabolism to GSH, H(2)S, and taurine, with special emphasis on therapeutic and nutritional use of L-cysteine to improve the health and well-being of animals and humans.