Chemical aspects of hydrogen sulfide measurements in physiological samples

Dietary and Endocrine Regulation of Endogenous Hydrogen Sulfide Production: Implications for Longevity

SIGNIFICANCE

Hydrogen sulfide (H₂S) at the right concentration is associated with numerous health benefits in experimental organisms, ranging from protection from ischemia/reperfusion injury to life span extension. Given the considerable translation potential, two major strategies have emerged: supplementation of exogenous H₂S and modulation of endogenous H₂S metabolism. Recent Advances: Recently, it was reported that hepatic H₂S production capacity is increased in two of the best-characterized mammalian models of life span extension, dietary restriction, and hypopituitary dwarfism, leading to new insights into dietary and hormonal regulation of endogenous H₂S production together with broader changes in sulfur amino acid (SAA) metabolism with implications for DNA methylation and redox status.

CRITICAL ISSUES

Here, we discuss the role of dietary SAAs and growth hormone (GH)/thyroid hormone (TH) signaling in regulation of endogenous H₂S production largely via repression of H₂S generating enzymes cystathionine γ-lyase (CGL) and cystathionine β-synthase (CBS) on the level of gene transcription, as well as reciprocal regulation of GH and TH signaling by H₂S itself. We also discuss plasticity of CGL and CBS gene expression in response to environmental stimuli and the potential of the microbiome to impact overall H₂S levels.

FUTURE DIRECTIONS

The relative contribution of increased H₂S to health span or lifespan benefits in models of extended longevity remains to be determined, as does the mechanism by which such benefits occur. Nonetheless, our ability to control H₂S levels using exogenous H₂S donors or by modifying the endogenous H₂S production/consumption equilibrium has the potential to improve health and increase "shelf-life" across evolutionary boundaries, including our own. Antioxid. Redox Signal. 28, 1483-1502.

MiR-125b-5p is involved in oxygen and glucose deprivation injury in PC-12 cells via CBS/H2S pathway

AIMS

Ischemic stroke is one of the leading causes of death worldwide. MicroRNAs (miRNAs) have been reported to be implicated in cerebral hypoxia injury and could serve as a therapeutic target. As the third gasotransmitter, hydrogen sulfide (H₂S) plays a critical role in hypoxia-induced injury in the central nervous system. Cystathionine β-synthase (CBS) is the main enzyme catalyzing the production of H₂S in brain. The objective of this study was to investigate the effect of miR-125b-5p on protecting against oxygen and glucose deprivation (OGD) injury in PC-12 cells by regulating CBS and H₂S generation.

RESULTS

The level of miR-125b-5p was increased in the rat MCAO model as well as OGD model in PC-12 cells. Meanwhile, CBS expression was remarkably downregulated. Overexpression of miR-125b-5p reduced CBS expression, decreased the H₂S generation, and deteriorated OGD injury in PC-12 cells. On the contrary, silencing miR-125b-5p protected PC-12 cells from OGD injury by upregulated CBS and H₂S levels. We found the protective effect of miR-125b-5p inhibition was associated with anti-oxidative and anti-apoptotic cell signaling through decreasing ROS level and reducing mitochondrial membrane potential (ΔΨm). Furthermore, the protective effect was absent when CBS was knockdown in PC-12 cells.

INNOVATION AND CONCLUSION

Our research discovered the regulation of CBS by miR-125b-5p. Besides, we provide the evidence for the therapeutic potential of miR-125b-5p inhibition for cerebral ischemia via CBS/H₂S pathway.

Clinical and Experimental Evidences of Hydrogen Sulfide Involvement in Lead-Induced Hypertension

Lead- (Pb-) induced hypertension has been shown in humans and experimental animals and cardiovascular effects of hydrogen sulfide (H₂S) have been reported previously. However, no studies examined involvement of H₂S in Pb-induced hypertension. We found increases in diastolic blood pressure and mean blood pressure in Pb-intoxicated humans followed by diminished H₂S plasmatic levels. In order to expand our findings, male Wistar rats were divided into four groups: Saline, Pb, NaHS, and Pb + NaHS. Pb-intoxicated animals received intraperitoneally (i.p.) 1st dose of 8 μg/100 g of Pb acetate and subsequent doses of 0.1 μg/100 g for seven days and sodium hydrosulfide- (NaHS-) treated animals received i.p. NaHS injections (50 μmol/kg/twice daily) for seven days. NaHS treatment blunted increases in systolic blood pressure, increased H₂S plasmatic levels, and diminished whole-blood lead levels. Treatment with NaHS in Pb-induced hypertension seems to induce a protective role in rat aorta which is dependent on endothelium and seems to promote non-NO-mediated relaxation. Pb-intoxication increased oxidative stress in rats, while treatment with NaHS blunted increases in plasmatic MDA levels and increased antioxidant status of plasma. Therefore, H₂S pathway may be involved in Pb-induced hypertension and treatment with NaHS exerts antihypertensive effect, promotes non-NO-mediated relaxation, and decreases oxidative stress in rats with Pb-induced hypertension.

A robust and versatile mass spectrometry platform for comprehensive assessment of the thiol redox metabolome

Several diseases are associated with perturbations in redox signaling and aberrant hydrogen sulfide metabolism, and numerous analytical methods exist for the measurement of the sulfur-containing species affected. However, uncertainty remains about their concentrations and speciation in cells/biofluids, perhaps in part due to differences in sample processing and detection principles. Using ultrahigh-performance liquid chromatography in combination with electrospray-ionization tandem mass spectrometry we here outline a specific and sensitive platform for the simultaneous measurement of 12 analytes, including total and free thiols, their disulfides and sulfide in complex biological matrices such as blood, saliva and urine. Total assay run time is < 10 min, enabling high-throughput analysis. Enhanced sensitivity and avoidance of artifactual thiol oxidation is achieved by taking advantage of the rapid reaction of sulfhydryl groups with N-ethylmaleimide. We optimized the analytical procedure for detection and separation conditions, linearity and precision including three stable isotope labelled standards. Its versatility for future more comprehensive coverage of the thiol redox metabolome was demonstrated by implementing additional analytes such as methanethiol, N-acetylcysteine, and coenzyme A. Apparent plasma sulfide concentrations were found to vary substantially with sample pretreatment and nature of the alkylating agent. In addition to protein binding in the form of mixed disulfides (S-thiolation) a significant fraction of aminothiols and sulfide appears to be also non-covalently associated with proteins. Methodological accuracy was tested by comparing the plasma redox status of 10 healthy human volunteers to a well-established protocol optimized for reduced/oxidized glutathione. In a proof-of-principle study a deeper analysis of the thiol redox metabolome including free reduced/oxidized as well as bound thiols and sulfide was performed. Additional determination of acid-labile sulfide/thiols was demonstrated in human blood cells, urine and saliva. Using this simplified mass spectrometry-based workflow the thiol redox metabolome can be determined in samples from clinical and translational studies, providing a novel prognostic/diagnostic platform for patient stratification, drug monitoring, and identification of new therapeutic approaches in redox diseases.

Chemical Biology of H2S Signaling through Persulfidation

Signaling by H2S is proposed to occur via persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH). Persulfidation provides a framework for understanding the physiological and pharmacological effects of H2S. Due to the inherent instability of persulfides, their chemistry is understudied. In this review, we discuss the biologically relevant chemistry of H2S and the enzymatic routes for its production and oxidation. We cover the chemical biology of persulfides and the chemical probes for detecting them. We conclude by discussing the roles ascribed to protein persulfidation in cell signaling pathways.

N-Acetyl Cysteine Functions as a Fast-Acting Antioxidant by Triggering Intracellular H2S and Sulfane Sulfur Production

The cysteine prodrug N-acetyl cysteine (NAC) is widely used as a pharmacological antioxidant and cytoprotectant. It has been reported to lower endogenous oxidant levels and to protect cells against a wide range of pro-oxidative insults. As NAC itself is a poor scavenger of oxidants, the molecular mechanisms behind the antioxidative effects of NAC have remained uncertain. Here we show that NAC-derived cysteine is desulfurated to generate hydrogen sulfide, which in turn is oxidized to sulfane sulfur species, predominantly within mitochondria. We provide evidence suggesting the possibility that sulfane sulfur species produced by 3-mercaptopyruvate sulfurtransferase and sulfide:quinone oxidoreductase are the actual mediators of the immediate antioxidative and cytoprotective effects provided by NAC.

Generation of controllable gaseous H2S concentrations using microfluidics

Hydrogen sulfide (H₂S) plays an important role as an intercellular and intracellular signaling molecule, yet its targets are not well understood. As a molecule it easily evaporates and it is hard to acquire stable concentration for in vitro studies, constituting a major problem for the field to identify its downstream targets and function. Here we develop a microfluidic system that can provide consistent and controllable H₂S levels in contrast to the current method of delivering large bolus doses to cells. The system relies on the permeability of H₂S gas through a polydimethylsiloxane thin membrane. A hydrogen sulfide donor, sodium hydrosulfide, is perfused in the microchannels below the gas permeable membrane and gaseous H₂S diffuses across the membrane, providing a stable concentration for up to 5 hours. Using electrochemical sensors within 3 ppm range, we found that H₂S concentration was dependent on two parameters, the concentration of H₂S donor, sodium hydrosulfide and the flow rate of the solution in the microchannels. Additionally, different H₂S concentration profiles can be obtained by alternating the flow rate, providing an easy means to control the H₂S concentration. Our approach constitutes a unique method for H₂S delivery for in vitro and ex vivo studies and is ideally suited to identify novel biological processes and cellular mechanisms regulated by H₂S.

A practical guide to working with H2S at the interface of chemistry and biology

Hydrogen sulfide (H₂S) is the most recently accepted endogenously produced gasotransmitter and is now implicated in a variety of physiological functions. In this tutorial review, our goal is to provide researchers new to the field of H₂S chemical biology with practical considerations, pitfalls, and best practices to enable smooth entry into investigations focused on biological H₂S. We present practical handling and safety considerations for working with this reactive biomolecule, and cover basic roles of H₂S biogenesis and action. Experimental methods for modulating H₂S levels, including enzymatic knockout, RNA silencing, enzymatic inhibition, and use of small molecule H₂S donors are highlighted. Complementing H₂S modulation techniques, we also highlight current strategies for H₂S detection and quantification.

Chemical methods for mapping cysteine oxidation

Methods to characterise oxidative modifications of cysteine help clarify their role in protein function in both healthy and diseased cells.

An isophorone-based far-red emitting ratiometric fluorescent probe for selective sensing and imaging of polysulfides

An isophorone-based far-red emitting fluorescent probe (RPHS1) for selective ratiometric sensing and imaging of H₂S_n in living cells was reported.

Engineered (Lys)6-Tagged Recombinant Sulfide-Reactive Hemoglobin I for Covalent Immobilization at Multiwalled Carbon Nanotubes

The recombinant HbI was fused with a poly-Lys tag ((Lys)₆-tagged rHbI) for specific-site covalent immobilization on two carbon nanotube transducer surfaces, i.e., powder and vertically aligned carbon nanotubes. The immobilization was achieved by following two steps: (1) generation of amine-reactive ester from the carboxylic acid groups of the surfaces and (2) coupling these groups with the amine groups of the Lys-tag. We analyzed the immobilization process using different conditions and techniques to differentiate protein covalent attachment from physical adsorption. Fourier transform infrared microspectroscopy data showed a 14 cm^-1 displacement of the protein's amide I and amide II peaks to lower the frequency after immobilization. This result indicates a covalent attachment of the protein to the surface. Differences in the morphology of the carbon substrate with and without (Lys)₆-tagged rHbI confirmed protein immobilization, as observed by transmission electron microscopy. The electrochemical studies, which were performed to evaluate the redox center of the immobilized protein, show a confinement suitable for an efficient electron transfer system. More importantly, the electrochemical studies allowed determination of a redox potential for the new (Lys)₆-tagged rHbI. The data show that the protein is electrochemically active and retains its biological activity toward H₂S.

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

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

Fe(III) - Sulfide interaction in globins: Characterization and quest for a putative Fe(IV)-sulfide species

The present study reports findings regarding the contrast between H₂S interaction with bovine hemoglobin (Hb) and horse heart myoglobin (Mb), in terms of binding and dissociation kinetics, affinities, and mechanism. At pH9.5, oxidation of ferric-sulfide adducts in presence of no free sulfide, using hexachloroiridate as oxidant is examined using stopped-flow UV-vis, EPR, vibrational spectroscopy and mass spectrometry. Oxidation of the ferric-sulfide adduct in such conditions occurs with a putative unstable Fe(IV)-sulfide adduct as intermediate that finally leads to a paramagnetic ferric species with distinct EPR features. As detected by MS spectrometry, this final species appears to be a truncated form of globin at a distinct Tyr. In case of Hb, only β-chain is truncated at Tyr144.

The mechanism of action and role of hydrogen sulfide in the control of vascular tone

Our knowledge about hydrogen sulfide (H₂S) significantly changed over the last two decades. Today it is considered as not only a toxic gas but also as a gasotransmitter with diverse roles in different physiological and pathophysiological processes. H₂S has pleiotropic effects and its possible mechanisms of action involve (1) a reversible protein sulfhydration which can alter the function of the modified proteins similar to nitrosylation or phosphorylation; (2) direct antioxidant effects and (3) interaction with metalloproteins. Its effects on the human cardiovascular system are especially important due to the high prevalence of hypertension and myocardial infarction. The exact molecular targets that affect the vascular tone include the K_ATP channel, the endothelial nitric oxide synthase, the phosphodiesterase of the vascular smooth muscle cell and the cytochrome c oxidase among others and the combination of all these effects lead to the final result on the vascular tone. The relative role of each effect depends immensely on the used concentration and also on the used donor molecules but several other factors and experimental conditions could alter the final effect. The aim of the current review is to give a comprehensive summary of the current understanding on the mechanism of action and role of H₂S in the regulation of vascular tone and to outline the obstacles that hinder the better understanding of its effects.

Hydrogen Polysulfide Biosignal-Responsive Polymersomes as a Nanoplatform for Distinguishing Intracellular Reactive Sulfur Species (RSS)

Reactive sulfur species (RSS) are a family of crucial biosignals for regulating cell processes. Among these, hydrogen polysulfide (H₂ S_n , n ≥ 2) is a hallmark of tumor suppressor activation and regarded as the actual regulator to mediate sulfur-related biology. However, high effective recognition of intracellular H₂ S_n is insurmountable due to its extremely low concentration and the disturbance of RSS analogues. Here an H₂ S_n -responsive macromolecule that can distinguish H₂ S_n from intracellular RSS through polymer degradation in ultrasensitive and highly selective manner is reported. This kind of polymers can further self-assemble into vesicular nanostructure. Upon cell uptake, they can be function as "all-in-one" H₂ S_n -nanoplatforms, in order to fulfill multiple ambitious tasks including monitoring the H₂ S_n biosynthetic pathways, unraveling the puzzles of H₂ S_n -mediated cellular events, and conducting H₂ S_n pathological milieu-specific drug delivery.

Polysulfides and products of H2S/S-nitrosoglutathione in comparison to H2S, glutathione and antioxidant Trolox are potent scavengers of superoxide anion radical and produce hydroxyl radical by decomposition of H2O2

Exogenous and endogenously produced sulfide derivatives, such as H₂S/HS^-/S^2-, polysulfides and products of the H₂S/S-nitrosoglutathione interaction (S/GSNO), affect numerous biological processes in which superoxide anion (O₂^-) and hydroxyl (OH) radicals play an important role. Their cytoprotective-antioxidant and contrasting pro-oxidant-toxic effects have been reported. Therefore, the aim of our work was to contribute to resolving this apparent inconsistency by studying sulfide derivatives/free radical interactions and their consequent biological effects compared to the antioxidants glutathione (GSH) and Trolox. Using the electron paramagnetic resonance (EPR) spin trapping technique and O₂^-, we found that a polysulfide (Na₂S₄) and S/GSNO were potent scavengers of O₂^- and cPTIO radicals compared to H₂S (Na₂S), GSH and Trolox, and S/GSNO scavenged the DEPMPO-OH radical. As detected by the EPR spectra of DEPMPO-OH, the formation of OH in physiological solution by S/GSNO was suggested. All the studied sulfide derivatives, but not Trolox or GSH, had a bell-shaped potency to decompose H₂O₂ and produced OH in the following order: S/GSNO > Na₂S₄ ≥ Na₂S > GSH = Trolox = 0, but they scavenged OH at higher concentrations. In studies of the biological consequences of these sulfide derivatives/H₂O₂ properties, we found the following: (i) S/GSNO alone and all sulfide derivatives in the presence of H₂O₂ cleaved plasmid DNA; (ii) S/GSNO interfered with viral replication and consequently decreased the infectivity of viruses; (iii) the sulfide derivatives induced apoptosis in A2780 cells but inhibited apoptosis induced by H₂O₂; and (iv) Na₂S₄ modulated intracellular calcium in A87MG cells, which depended on the order of Na₂S₄/H₂O₂ application. We suggest that the apparent inconsistency of the cytoprotective-antioxidant and contrasting pro-oxidant-toxic biological effects of sulfide derivatives results from their time- and concentration-dependent radical production/scavenging properties and their interactions with O₂^-, OH and H₂O₂. The results imply a direct involvement of sulfide derivatives in O₂^- and H₂O₂/OH free radical pathways modulating antioxidant/toxic biological processes.

Rapid Antidepressant Effect of Hydrogen Sulfide: Evidence for Activation of mTORC1-TrkB-AMPA Receptor Pathways

AIMS

We asked whether hydrogen sulfide (H₂S), as the third gaseous mediator, provided fast antidepressant effect on major depressive disorders and underlying mechanisms.

RESULTS

The decreased level of H₂S was detected in the hippocampus of chronic unpredictable mild stress (CUMS)-treated rats. Acute administration of H₂S either by H₂S inhalation or by the donor NaHS produced a rapid antidepressant-like behavioral effect. Further investigation demonstrated that this effect of H₂S was mediated by reversing the CUMS-induced decrease in dendritic spine density and required the activation of mammalian target of rapamycin (mTOR)C1 and neurotrophic TrkB receptors, which proceeded to increase synaptic protein expression, including postsynaptic density protein 95, synaptophysin, and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor GluR1/2 subunit.

INNOVATION

This study provides the first direct evidence for detecting the decreased H₂S in hippocampus of CUMS rats and the biological significance of H₂S in treating major depression.

CONCLUSION

Our data demonstrate that H₂S activates mTORC1 signaling cascades and thereby produces fast-onset antidepressant effect. The study provides a profound insight into H₂S or its donors as potent preventive and therapeutic agents for intervention of depression. Antioxid. Redox Signal. 27, 472-488.

Metabolomic Evaluation of the Consequences of Plasma Cystathionine Elevation in Adults with Stable Angina Pectoris

Background: An elevated circulating cystathionine concentration, which arises in part from insufficiencies of vitamin B-6, B-12, or folate, has been shown to be associated with cardiovascular disease (CVD) risk. Hydrogen sulfide (H₂S) is a gasotransmitter involved in vasodilation, neuromodulation, and inflammation. Most endogenously produced H₂S is formed by pyridoxal phosphate (PLP)-dependent enzymes by noncanonical reactions of the transsulfuration pathway that yield H₂S concurrently form lanthionine and homolanthionine. Thus, plasma lanthionine and homolanthionine concentrations can provide relative information about H₂S production in vivo.Objective: To determine the metabolic consequences of an elevated plasma cystathionine concentration in adults with stable angina pectoris (SAP), we conducted both targeted and untargeted metabolomic analyses.Methods: We conducted NMR and LC-mass spectrometry (MS) metabolomic analyses on a subset of 80 plasma samples from the Western Norway Coronary Angiography Cohort and selected, based on plasma cystathionine concentrations, a group with high cystathionine concentrations [1.32 ± 0.60 μmol/L (mean ± SD); n = 40] and a group with low cystathionine concentrations [0.137 ± 0.011 μmol/L (mean ± SD); n = 40]. Targeted and untargeted metabolomic analyses were performed and assessed with the use of Student's t tests corrected for multiple testing. Overall differences between the cystathionine groups were assessed by untargeted NMR and LC-MS metabolomic methods and evaluated by partial least squares discriminant analysis (PLS-DA) with significant discriminating metabolites identified with 99% confidence.Results: Subjects with high cystathionine concentrations had 75% higher plasma lanthionine concentrations (0.12 ± 0.044 μmol/L) than subjects with low cystathionine concentrations [0.032 ± 0.013 μmol/L (P < 0.001)]. Although plasma homolanthionine concentrations were notably higher than lanthionine concentrations, they were not different between the groups (P = 0.47). PLS-DA results showed that a high plasma cystathionine concentration in SAP was associated with higher glucose, branched-chain amino acids, and phenylalanine concentrations, lower kidney function, and lower glutathione and plasma PLP concentrations due to greater catabolism. The high-cystathionine group had a greater proportion of subjects in the postprandial state.Conclusion: These data suggest that metabolic perturbations consistent with higher CVD risk exist in SAP patients with elevated plasma cystathionine concentrations.

A rapid evaluation of acute hydrogen sulfide poisoning in blood based on DNA-Cu/Ag nanocluster fluorescence probe

Hydrogen sulfide (H₂S) is a highly toxic gas as a cause of inhalational death. Accurate detection of H₂S poisoning concentration is valuable and vital for forensic workers to estimate the cause of death. But so far, it is no uniform and reliable standard method to measure sulfide concentrations in H₂S poisoning blood for forensic identification. This study introduces a fluorescence sensing technique into forensic research, in which a DNA-templated copper/silver nanocluster (DNA-Cu/AgNCs) fluorescence probe has been proposed to selective detection of S^2-. Under an optimized condition, the proposed method can allow for determination of S^2- in the concentration range of 10 pM to 1 mM with a linear equation: y = -0.432 lg[S^2-] + 0.675 (R² = 0.9844), with the limit of detection of 3.75 pM. Moreover, acute H₂S poisoning mouse models were established by intraperitoneally injected different doses of Na₂S, and the practical feasibility of the proposed fluorescence sensor has been demonstrated by 35 poisoning blood samples. This proposed method is proved to be quite simple and straightforward for the detection of H₂S poisoning blood. Also it may provide a basis for sulfide metabolizing study in body, and it would be meaningful to further push forensic toxicology identification and clinical laboratory research.

Cysteine Addition Promotes Sulfide Production and 4-Fold Hg(II)-S Coordination in Actively Metabolizing Escherichia coli

The bacterial uptake of mercury(II), Hg(II), is believed to be energy-dependent and is enhanced by cysteine in diverse species of bacteria under aerobic and anaerobic conditions. To gain insight into this Hg(II) biouptake pathway, we have employed X-ray absorption spectroscopy (XAS) to investigate the relationship between exogenous cysteine, cellular metabolism, cellular localization, and Hg(II) coordination in aerobically respiring Escherichia coli (E. coli). We show that cells harvested in exponential growth phase consistently display mixtures of 2-fold and 4-fold Hg(II) coordination to sulfur (Hg-S₂ and Hg-S₄), with added cysteine enhancing Hg-S₄ formation. In contrast, cells in stationary growth phase or cells treated with a protonophore causing a decrease in cellular ATP predominantly contain Hg-S₂, regardless of cysteine addition. Our XAS results favor metacinnabar (β-HgS) as the Hg-S₄ species, which we show is associated with both the cell envelope and cytoplasm. Additionally, we observe that added cysteine abiotically oxidizes to cystine and exponentially growing E. coli degrade high cysteine concentrations (100-1000 μM) into sulfide. Thermodynamic calculations confirm that cysteine-induced sulfide biosynthesis can promote the formation of dissolved and particulate Hg(II)-sulfide species. This report reveals new complexities arising in Hg(II) bioassays with cysteine and emphasizes the need for considering changes in chemical speciation as well as growth stage.

New method for quantification of gasotransmitter hydrogen sulfide in biological matrices by LC-MS/MS

Hydrogen sulfide exists widely in mammalian tissues and plays a vital role in physiological and pathophysiological processes. However, striking differences with orders of magnitude were observed for the detected hydrogen sulfide concentrations in biological matrices among different measurements in literature, which lead to the uncertainty for examination the biological relevance of hydrogen sulfide. Here, we developed and validated a liquid chromatography- mass spectrometry (LC-MS/MS) method for the determination of hydrogen sulfide in various biological matrices by determination of a derivative of hydrogen sulfide and monobromobimane named sulfide dibimane (SDB). ³⁶S-labeled SDB was synthesized and validated for using as an internal standard. This method has been successfully used to measure hydrogen sulfide levels in a broad range of biological matrices, such as blood, plasma, tissues, cells, and enzymes, across different species. Moreover, a novel mode that hydrogen sulfide could loosely and non-covalently bind to human serum protein (HSA) and hemoglobin (HB) was revealed by using the developed method.

Engineering bacterial thiosulfate and tetrathionate sensors for detecting gut inflammation

There is a groundswell of interest in using genetically engineered sensor bacteria to study gut microbiota pathways, and diagnose or treat associated diseases. Here, we computationally identify the first biological thiosulfate sensor and an improved tetrathionate sensor, both two‐component systems from marine Shewanella species, and validate them in laboratory Escherichia coli. Then, we port these sensors into a gut‐adapted probiotic E. coli strain, and develop a method based upon oral gavage and flow cytometry of colon and fecal samples to demonstrate that colon inflammation (colitis) activates the thiosulfate sensor in mice harboring native gut microbiota. Our thiosulfate sensor may have applications in bacterial diagnostics or therapeutics. Finally, our approach can be replicated for a wide range of bacterial sensors and should thus enable a new class of minimally invasive studies of gut microbiota pathways.

Toward Hydrogen Sulfide Based Therapeutics: Critical Drug Delivery and Developability Issues

Hydrogen sulfide (H₂ S), together with nitric oxide (NO) and carbon monoxide (CO), belongs to the gasotransmitter family and plays important roles in mammals as a signaling molecule. Many studies have also shown the various therapeutic effects of H₂ S, which include protection against myocardial ischemia injury, cytoprotection against oxidative stress, mediation of neurotransmission, inhibition of insulin signaling, regulation of inflammation, inhibition of the hypoxia-inducible pathway, and dilation of blood vessels. One major challenge in the development of H₂ S-based therapeutics is its delivery. In this manuscript, we assess the various drug delivery strategies in the context of being used research tools and eventual developability as therapeutic agents.

Analgesic effect of dimethyl trisulfide in mice is mediated by TRPA1 and sst4 receptors

TRPA1 receptors are calcium-permeable ligand-gated channels expressed in primary sensory neurons and involved in inflammation and pain. Activation of these neurons might have analgesic effect. Suggested mechanism of analgesic effect mediated by TRPA1 activation is the release of somatostatin (SOM) and its action on sst₄ receptors. In the present study analgesic effect of TRPA1 activation on primary sensory neurons by organic trisulfide compound dimethyl trisulfide (DMTS) presumably leading to SOM release was investigated. Opening of TRPA1 by DMTS in CHO cells was examined by patch-clamp and fluorescent Ca²⁺ detection. Ca²⁺ influx upon DMTS administration in trigeminal ganglion (TRG) neurons of TRPA1 receptor wild-type (WT) and knockout (KO) mice was detected by ratiometric Ca²⁺ imaging. SOM release from sensory nerves of murine skin was assessed by radioimmunoassay. Analgesic effect of DMTS in mild heat injury-induced mechanical hyperalgesia was examined by dynamic plantar aesthesiometry. Regulatory role of DMTS on deep body temperature (T_b) was measured by thermocouple thermometry with respirometry and by telemetric thermometry. DMTS produced TRPA1-mediated currents and elevated [Ca²⁺]_i in CHO cells. Similar data were obtained in TRG neurons. DMTS released SOM from murine sensory neurons TRPA1-dependently. DMTS exerted analgesic effect mediated by TRPA1 and sst₄ receptors. DMTS-evoked hypothermia and hypokinesis were attenuated in freely-moving TRPA1 KO animals. Our study has presented original evidence regarding analgesic action of DMTS which might be due to TRPA1-mediated SOM release from sensory neurons and activation of sst₄ receptors. DMTS could be a novel analgesic drug candidate.

A NIR fluorescent chemodosimeter for imaging endogenous hydrogen polysulfides via the CSE enzymatic pathway

Sodium polysulfides (Na₂S_n, n > 1) as important raw materials in the chemical industry can afford hydrogen polysulfides (H₂S_n, n > 1) under physiological conditions.

Clinical Implication of Plasma Hydrogen Sulfide Levels in Japanese Patients with Type 2 Diabetes

Objective The goal of the present study was to investigate the plasma hydrogen sulfide (H₂S) levels in patients with type 2 diabetes, as the plasma H₂S levels in Japanese patients with type 2 diabetes remain unclear. Methods The plasma H₂S levels were measured in 154 outpatients with type 2 diabetes and 66 outpatients without diabetes. All blood samples were collected in the outpatient department from 09:00 to 10:00. The patients had fasted from 21:00 the previous evening and had not consumed alcohol or caffeine or smoked until sample collection. The plasma H₂S levels were measured using the methylene blue assay. The plasma H₂S levels were determined in triplicate, and the average concentrations were calculated against a calibration curve of sodium sulfide. Results The patients with type 2 diabetes showed a progressive reduction in the plasma H₂S levels (45.115.5 M versus 54.026.4 M, p<0.05), which paralleled poor glycemic control. There was a significant correlation between a reduction in the plasma H₂S levels and the HbA1c levels (=-0.505, p<0.01), Furthermore, a reduction in the plasma H₂S levels was found to be related to a history of cardiovascular diseases in patients with type 2 diabetes (39.913.8 M versus 47.515.9 M, p<0.01). Conclusion Collectively, the plasma H₂S levels were reduced in patients with type 2 diabetes, which may have implications in the pathophysiology of cardiovascular disease in diabetic patients. The trial was registered with the University Hospital Medical Information Network (UMIN no. #000020549).

Sulfur Atom in its Bound State Is a Unique Element Involved in Physiological Functions in Mammals

It was in the 1950s that the term polysulfide or persulfide was introduced in biological studies. The unfamiliar term “sulfane sulfur” sometimes appeared in papers published in the 1970s, and was defined in the review article by Westley in 1983. In the article, sulfane sulfur is described as sulfur atoms that are covalently bound only with sulfur atoms, and as this explanation was somewhat difficult to comprehend, it was not generally accepted. Thus, in the early 1990s, we redefined these sulfur species as “bound sulfur”, which easily converts to hydrogen sulfide on reduction with a thiol reducing agent. In other words, bound sulfur refers to a sulfur atom that exists in a zero to divalent form (0 to −2). The first part of this review focuses on the fluorescent derivatization HPLC method—which we developed for measurement of bound sulfur—and explains the distribution of bound sulfur and the hydrogen sulfide-producing ability of various tissues, as clarified by this method. Next, we discuss diverse physiological functions and involvement of polysulfide, a typical type of bound sulfur, in the redox regulation system. Additionally, we also address its possible physiological role in the central nervous system, based on its action of scavenging reactive carbonyl compounds.

Hydrogen sulfide, an enhancer of vascular nitric oxide signaling: mechanisms and implications

Nitric oxide (NO) vascular signaling has long been considered an independent, self-sufficient pathway. However, recent data indicate that the novel gaseous mediator, hydrogen sulfide (H₂S), serves as an essential enhancer of vascular NO signaling. The current article overviews the multiple levels at which this enhancement takes place. The first level of interaction relates to the formation of biologically active hybrid S/N species and the H₂S-induced stimulation of NO release from its various stable "pools" (e.g., nitrite). The next interactions occur on the level of endothelial calcium mobilization and PI3K/Akt signaling, increasing the specific activity of endothelial NO synthase (eNOS). The next level of interaction occurs on eNOS itself; H₂S directly interacts with the enzyme: sulfhydration of critical cysteines stabilizes it in its physiological, dimeric state, thereby optimizing eNOS-derived NO production and minimizing superoxide formation. Yet another level of interaction, further downstream, occurs at the level of soluble guanylate cyclase (sGC): H₂S stabilizes sGC in its NO-responsive, physiological, reduced form. Further downstream, H₂S inhibits the vascular cGMP phosphodiesterase (PDE5), thereby prolonging the biological half-life of cGMP. Finally, H₂S-derived polysulfides directly activate cGMP-dependent protein kinase (PKG). Taken together, H₂S emerges an essential endogenous enhancer of vascular NO signaling, contributing to vasorelaxation and angiogenesis. The functional importance of the H₂S/NO cooperative interactions is highlighted by the fact that H₂S loses many of its beneficial cardiovascular effects when eNOS is inactive.

Nitrosopersulfide (SSNO-) targets the Keap-1/Nrf2 redox system

Nitric oxide (NO), hydrogen sulfide and polysulfides have been proposed to contribute to redox signaling by activating the Keap-1/Nrf2 stress response system. Nitrosopersulfide (SSNO^-) recently emerged as a bioactive product of the chemical interaction of NO or nitrosothiols with sulfide; upon decomposition it generates polysulfides and free NO, triggering the activation of soluble guanylate cyclase, inducing blood vessel relaxation in vitro and lowering blood pressure in vivo. Whether SSNO^- itself interacts with the Keap-1/Nrf2 system is unknown. We therefore sought to investigate the ability of SSNO^- to activate Nrf2-dependent processes in human vascular endothelial cells, and to compare the pharmacological effects of SSNO^- with those of its precursors NO and sulfide at multiple levels of target engagement. We here demonstrate that SSNO^- strongly increases nuclear levels, binding activity and transactivation activity of Nrf2, thereby increasing mRNA expression of Hmox-1, the gene encoding for heme oxygenase 1, without adversely affecting cell viability. Under all conditions, SSNO^- appeared to be more potent than its parent compounds, NO and sulfide. SSNO^--induced Nrf2 transactivation activity was abrogated by either NO scavenging with cPTIO or inhibition of thiol sulfuration by high concentrations of cysteine, implying a role for both persulfides/polysulfides and NO in SSNO^- mediated Nrf2 activation. Taken together, our studies demonstrate that the Keap-1/Nrf2 redox system is a biological target of SSNO^-, enriching the portfolio of bioactivity of this vasoactive molecule to also engage in the regulation of redox signaling processes. The latter suggests a possible role as messenger and/or mediator in cellular sensing and adaptations processes.

H2S concentrations in the heart after acute H2S administration: methodological and physiological considerations

In this study, we have tried to characterize the limits of the approach typically used to determine H₂S concentrations in the heart based on the amount of H₂S evaporating from heart homogenates-spontaneously, after reaction with a strong reducing agent, or in a very acidic solution. Heart homogenates were prepared from male rats in control conditions or after H₂S infusion induced a transient cardiogenic shock (CS) or cardiac asystole (CA). Using a method of determination of gaseous H₂S with a detection limit of 0.2 nmol, we found that the process of homogenization could lead to a total disappearance of free H₂S unless performed in alkaline conditions. Yet, after restoration of neutral pH, free H₂S concentration from samples processed in alkaline and nonalkaline milieus were similar and averaged ∼0.2-0.4 nmol/g in both control and CS homogenate hearts and up to 100 nmol/g in the CA group. No additional H₂S was released from control, CS, or CA hearts by using the reducing agent tris(2-carboxyethyl)phosphine or a strong acidic solution (pH < 2) to "free" H₂S from combined pools. Of note, the reducing agent DTT produced a significant sulfide artifact and was not used. These data suggest that 1) free H₂S found in heart homogenates is not a reflection of H₂S present in a "living" heart and 2) the pool of combined sulfides, released in a strong reducing or acidic milieu, does not increase in the heart in a measurable manner even after toxic exposure to sulfide.

Highly Selective and Sensitive One- and Two-Photon Ratiometric Fluorescent Probe for Intracellular Hydrogen Polysulfide Sensing

Hydrogen polysulfide (H2Sn) has attracted increasing attention due to the fact that it is actually the key signaling molecule rather than hydrogen sulfide (H2S). Therefore, developing a sensitive and accurate assay to investigate the biosynthetic pathways of H2Sn is of physiological and pathological significance. In this work, based on the commonly used two-photon fluorophore, 1,8-naphthalimide, a new probe, NRT-HP, has been designed and synthesized that displayed both one- and two-photon ratiometric fluorescence changes toward H2Sn via H2Sn-mediated benzodithiolone formation. NRT-HP exhibits excellent pH stability, high selectivity and low detection limit (0.1 μM) in aqueous media. Furthermore, two-photon fluorescence microscopy experiments have demonstrated that NRT-HP could be used for the H2Sn detection in live cells as well as tissue slices.

Gasotransmitters in Vascular Complications of Diabetes

In the past decades three gaseous signaling molecules-so-called gasotransmitters-have been identified: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S). These gasotransmitters are endogenously produced by different enzymes in various cell types and play an important role in physiology and disease. Despite their specific functions, all gasotransmitters share the capacity to reduce oxidative stress, induce angiogenesis, and promote vasorelaxation. In patients with diabetes, a lower bioavailability of the different gasotransmitters is observed when compared with healthy individuals. As yet, it is unknown whether this reduction precedes or results from diabetes. The increased risk for vascular disease in patients with diabetes, in combination with the extensive clinical, financial, and societal burden, calls for action to either prevent or improve the treatment of vascular complications. In this Perspective, we present a concise overview of the current data on the bioavailability of gasotransmitters in diabetes and their potential role in the development and progression of diabetes-associated microvascular (retinopathy, neuropathy, and nephropathy) and macrovascular (cerebrovascular, coronary artery, and peripheral arterial diseases) complications. Gasotransmitters appear to have both inhibitory and stimulatory effects in the course of vascular disease development. This Perspective concludes with a discussion on gasotransmitter-based interventions as a therapeutic option.

Hydrogen Sulfide, Oxidative Stress and Periodontal Diseases: A Concise Review

In the past years, biomedical research has recognized hydrogen sulfide (H₂S) not only as an environmental pollutant but also, along with nitric oxide and carbon monoxide, as an important biological gastransmitter with paramount roles in health and disease. Current research focuses on several aspects of H₂S biology such as the biochemical pathways that generate the compound and its functions in human pathology or drug synthesis that block or stimulate its biosynthesis. The present work addresses the knowledge we have to date on H₂S production and its biological roles in the general human environment with a special focus on the oral cavity and its involvement in the initiation and development of periodontal diseases.

Thioethers as markers of hydrogen sulfide production in homocystinurias

Two enzymes in the transsulfuration pathway of homocysteine -cystathionine beta-synthase (CBS) and gamma-cystathionase (CTH)-use cysteine and/or homocysteine to produce the important signaling molecule hydrogen sulfide (H2S) and simultaneously the thioethers lanthionine, cystathionine or homolanthionine. In this study we explored whether impaired flux of substrates for H2S synthesis and/or deficient enzyme activities alter production of hydrogen sulfide in patients with homocystinurias. As an indirect measure of H2S synthesis we determined by LC-MS/MS concentrations of thioethers in plasma samples from 33 patients with different types of homocystinurias, in 8 patient derived fibroblast cell lines, and as reaction products of seven purified mutant CBS enzymes. Since chaperoned recombinant mutant CBS enzymes retained capacity of H2S synthesis in vitro it can be stipulated that deficient CBS activity in vivo may impair H2S production. Indeed, in patients with classical homocystinuria we observed significantly decreased cystathionine and lanthionine concentrations in plasma (46% and 74% of median control levels, respectively) and significantly lower cystathionine in fibroblasts (8% of median control concentrations) indicating that H2S production from cysteine and homocysteine may be also impaired. In contrast, the grossly elevated plasma levels of homolanthionine in CBS deficient patients (32-times elevation compared to median of controls) clearly demonstrates a simultaneous overproduction of H2S from homocysteine by CTH. In the remethylation defects the accumulation of homocysteine and the increased flux of metabolites through the transsulfuration pathway resulted in elevation of cystathionine and homolanthionine (857% and 400% of median control values, respectively) indicating a possibility of an increased biosynthesis of H2S by both CBS and CTH. This study shows clearly disturbed thioether concentrations in homocystinurias, and modeling using these data indicates that H2S synthesis may be increased in these conditions. Further studies are needed to confirm our findings and to explore the possible implications for pathophysiology of these disorders.

A highly selective and sensitive near-infrared fluorescent probe for imaging of hydrogen sulphide in living cells and mice

Hydrogen sulphide (H₂S), the third endogenous gaseous signalling molecule, has attracted attention in biochemical research. The selective detection of H₂S in living systems is essential for studying its functions. Fluorescence detection methods have become useful tools to explore the physiological roles of H₂S because of their real-time and non-destructive characteristics. Herein we report a near-infrared fluorescent probe, NIR-HS, capable of tracking H₂S in living organisms. With high sensitivity, good selectivity and low cytotoxicity, NIR-HS was able to recognize both the exogenous and endogenous H₂S in living cells. More importantly, it realized the visualization of endogenous H₂S generated in cells overexpressing cystathionine β-synthase (CBS), one of the enzymes responsible for producing endogenous H₂S. The probe was also successfully applied to detect both the exogenous and endogenous H₂S in living mice. The superior sensing properties of the probe render it a valuable research tool in the H₂S-related medical research.

A novel persulfide detection method reveals protein persulfide- and polysulfide-reducing functions of thioredoxin and glutathione systems

Hydrogen sulfide signaling involves persulfide formation at specific protein Cys residues. However, overcoming current methodological challenges in persulfide detection and elucidation of Cys regeneration mechanisms from persulfides are prerequisites for constructing a bona fide signaling model. We here establish a novel, highly specific protein persulfide detection protocol, ProPerDP, with which we quantify 1.52 ± 0.6 and 11.6 ± 6.9 μg/mg protein steady-state protein persulfide concentrations in human embryonic kidney 293 (HEK293) cells and mouse liver, respectively. Upon treatment with polysulfides, HEK293 and A549 cells exhibited increased protein persulfidation. Deletion of the sulfide-producing cystathionine-γ-lyase or cystathionine-β-synthase enzymes in yeast diminished protein persulfide levels, thereby corroborating their involvement in protein persulfidation processes. We here establish that thioredoxin (Trx) and glutathione (GSH) systems can independently catalyze reductions of inorganic polysulfides and protein persulfides. Increased endogenous persulfide levels and protein persulfidation following polysulfide treatment in thioredoxin reductase-1 (TrxR1) or thioredoxin-related protein of 14 kDa (TRP14) knockdown HEK293 cells indicated that these enzymes constitute a potent regeneration system of Cys residues from persulfides in a cellular context. Furthermore, TrxR1-deficient cells were less viable upon treatment with toxic amounts of polysulfides compared to control cells. Emphasizing the dominant role of cytosolic disulfide reduction systems in maintaining sulfane sulfur homeostasis in vivo, protein persulfide levels were markedly elevated in mouse livers where hepatocytes lack both TrxR1 and glutathione reductase (TR/GR-null). The different persulfide patterns observed in wild-type, GR-null, and TR/GR-null livers suggest distinct roles for the Trx and GSH systems in regulating subsets of protein persulfides and thereby fine-tuning sulfide signaling pathways.

A flavylium-based turn-on fluorescent probe for imaging hydrogen polysulfides in living cells

A flavylium-based turn-on fluorescent probe for imaging of hydrogen polysulfides in living cells has been developed.

Electrochemical hydrogen sulfide biosensors

Biological application of electrochemical hydrogen sulfide sensors.