Activatable Small-Molecule Hydrogen Sulfide Donors

Regulating H2S release from self-assembled peptide H2S-donor conjugates using cysteine derivatives

Self-assembled peptides provide a modular and diverse platform for drug delivery, and innovative delivery methods are needed for delivery of hydrogen sulfide (H2S), an endogenous signaling molecule (gasotransmitter) with significant therapeutic potential. Of the available types of H2S donors, peptide/protein H2S donor conjugates (PHDCs) offer significant versatility. Here we discuss the design, synthesis, and in-depth study of a PHDC containing three covalently linked components: a thiol-triggered H2S donor based on an S-aroylthiooxime (SATO), a GFFF tetrapeptide, and a tetraethylene glycol (TEG) dendron. Conventional transmission electron microscopy showed that the PHDC self-assembled into spherical structures without heat or stirring, but it formed nanofibers with gentle heat (37 °C) and stirring. Circular dichroism (CD) spectroscopy data collected during self-assembly under nanofiber-forming conditions suggested an increase in β-sheet character and a decrease in organization of the SATO units. Release of H2S from the nanofibers was studied through triggering with various thiols. The release rate and total amount of H2S released over both short (5 h) and long (7 d) time scales varied with the charge state: negatively charged and zwitterionic thiols (e.g., Ac-Cys-OH and H-Cys-OH) triggered release slowly while a neutral thiol (Ac-Cys-OMe) showed ∼10-fold faster release, and a positively charged thiol (H-Cys-OMe) triggered H2S release nearly 50-fold faster than the negatively charged thiols. CD spectroscopy studies monitoring changes in secondary structure over time during H2S release showed similar trends. This study sheds light on the driving forces behind self-assembling nanostructures and offers insights into tuning H2S release through thiol charge state modulation.

Recent Developments On Activatable Turn-On Fluorogenic Donors of Hydrogen Sulfide (H2S)

Hydrogen sulfide (H2S) is considered the third member of the gasotransmitter family, along with nitric oxide (NO) and carbon monoxide (CO). Besides its role in physiological and pathophysiological conditions, the promising therapeutic potential of this small-molecule makes it advantageous for various pharmaceutical applications. The endogenous production of H2S at a lower concentration is crucial in maintaining redox balance and cellular homeostasis, and the dysregulation leads to various disease states. In the event of H2S deficiency, the exogenous donation of H2S could help maintain the optimal cellular concentration of H2S and cellular homeostasis. Over the last several years, researchers have developed numerous small-molecule non-fluorogenic organosulfur compounds as H2S donors and investigated their pharmacological potentials. However, reports on stimuli-responsive turn-on fluorogenic donors of H2S have appeared recently. Interestingly, the fluorogenic H2S donors offer additional advantages with the non-invasive real-time monitoring of the H2S release utilizing the simultaneous turn-on fluorogenic processes. The review summarizes the recent developments in turn-on fluorogenic donors of H2S and the potential biological applications that have developed over the years.

An Examination of Chemical Tools for Hydrogen Selenide Donation and Detection

Hydrogen selenide (H2Se) is an emerging biomolecule of interest with similar properties to that of other gaseous signaling molecules (i.e., gasotransmitters that include nitric oxide, carbon monoxide, and hydrogen sulfide). H2Se is enzymatically generated in humans where it serves as a key metabolic intermediate in the production of selenoproteins and other selenium-containing biomolecules. However, beyond its participation in biosynthetic pathways, its involvement in cellular signaling or other biological mechanisms remains unclear. To uncover its true biological significance, H2Se-specific chemical tools capable of functioning under physiological conditions are required but lacking in comparison to those that exist for other gasotransmitters. Recently, researchers have begun to fill this unmet need by developing new H2Se-releasing compounds, along with pioneering methods for selenide detection and quantification. In combination, the chemical tools highlighted in this review have the potential to spark groundbreaking explorations into the chemical biology of H2Se, which may lead to its branding as the fourth official gasotransmitter.

Transpersulfidation or H2S Release? Understanding the Landscape of Persulfide Chemical Biology

Persulfides (RSSH) are biologically important reactive sulfur species that are endogenously produced, protect key cysteine residues from irreversible oxidation, and are important intermediates during different enzymatic processes. Although persulfides are stronger nucleophiles than their thiol counterparts, persulfides can also act as electrophiles in their neutral, protonated form in specific environments. Moreover, persulfides are electrophilic at both sulfur atoms, and the reaction with a thiolate can lead to either H2S release with disulfide formation or alternatively result in transpersulfidation. Despite the broad acceptance of these reaction pathways, the specific properties that control whether persulfides react through the H2S-releasing or transpersulfidation pathway remain elusive. Herein, we use a combined computational and experimental approach to directly investigate the reactivity between persulfides and thiols to answer these questions. Using density functional theory (DFT) calculations, we demonstrate that increasing steric bulk or electron withdrawal near the persulfide can shunt persulfide reactivity through the transpersulfidation pathway. Building from these insights, we use a synthetic persulfide donor and an N-iodoacetyl l-tyrosine methyl ester (TME-IAM) trapping agent to experimentally monitor and measure transpersulfidation from a bulky penicillamine-based persulfide to a cysteine-based thiol, which, to the best of our knowledge, is the first direct observation of transpersulfidation between low-molecular-weight species. Taken together, these combined approaches highlight how the properties of persulfides are directly impacted by local environments, which has significant impacts in understanding the complex chemical biology of these reactive species.

An Expanded Palette of Fluorescent COS/H2S-Releasing Donors for H2S Delivery, Detection, and In Vivo Application

Hydrogen sulfide (H2S) is an important reactive sulfur species that is involved in many biological functions, and H2S imbalances have been indicated as a potential biomarker for various diseases. Different H2S donors have been developed to deliver H2S directly to biological systems, but few reports include donors with optical responses that allow for tracking of H2S release. Moreover, donor systems that use the same chemistry to deliver H2S across a palette of fluorescent responses remain lacking. Here we report five thiol-activated fluorescence turn-on COS/H2S donors that utilize blue, yellow, orange, red, and near infrared-emitting dyes functionalized with an H2S-releasing sulfenyl thiocarbonate scaffold. Upon treatment with thiols, each donor provides a fluorescence turn-on response (3-310-fold) and high H2S release efficiencies (>60 %). Using combined electrode and fluorescence experiments, we directly correlate the measured H2S release with the fluorescence response. All donors are biocompatible and release H2S in live cell environments. In addition, we demonstrate that the NIR donor allows for imaging H2S release in live rats via subcutaneous injection of the donor loaded into an alginate gel, which to the best of our knowledge is the first in vivo tracking of H2S release from a fluorogenic donor in non-transparent organisms.

Using mechanism-based combinations of H2S-donors to maximize the cardioprotective action of H2S

H2S-donors are cardioprotective in ischemia/reperfusion (I/R) injury. Some H2S-donors exert their beneficial effects in a nitric oxide (NO)-dependent manner, while others act using NO-independent pathways. The aims of the present study were to (i) evaluate whether H2S-donors with distinct pharmacodynamic properties act synergistically in I/R injury and (ii) determine if H2S-donors remain cardioprotective in obese mice. C57BL/6 mice were subjected to 30 min of ischemia followed by 120 min of reperfusion. Donors were administered intravenously at the end of ischemia (Na2S: 1 μmol/kg, GYY4137: 25 μmol/kg, AP39: 0,25 μmol/kg), while the 3-mercaptopyruvate sulfurtransferase (10 mg/kg) inhibitor was given intraperitonially 1 h prior to ischemia. Infarct size was estimated by 2,3,5-triphenyltetrazolium staining, while the area at risk was calculated using Evans blue. All three donors reduced infarct size when administered as a sole treatment. Co-administration of Na2S/GYY4137, as well as Na2S/AP39 reduced further the I/R injury, beyond what was observed with each individual donor. Since inhibition of the H2S-producing enzyme 3-mercaptopyruvate sulfurtransferase is known to reduce infarct size, we co-administered C3 with Na2S to determine possible additive effects between the two agents. In this case, combination of C3 with Na2S did not yield superior results compared to the individual treatments. Similarly, to what was observed in healthy mice, administration of a H2S-donor (Na2S or AP39) reduced I/R injury in mice rendered obese by consumption of a high fat diet. We conclude that combining a NO-dependent with a NO-independent H2S-donor leads to enhanced cardioprotection and that H2S-donors remain effective in obese animals.

Selenium-Based Catalytic Scavengers for Concurrent Scavenging of H2 S and Reactive Oxygen Species

Hydrogen sulfide (H2 S) is an endogenous gasotransmitter that plays important roles in redox signaling. H2 S overproduction has been linked to a variety of disease states and therefore, H2 S-depleting agents, such as scavengers, are needed to understand the significance of H2 S-based therapy. It is known that elevated H2 S can induce oxidative stress with elevated reactive oxygen species (ROS) formation, such as in H2 S acute intoxication. We explored the possibility of developing catalytic scavengers to simultaneously remove H2 S and ROS. Herein, we studied a series of selenium-based molecules as catalytic H2 S/H2 O2 scavengers. Inspired by the high reactivity of selenoxide compounds towards H2 S, 14 diselenide/monoselenide compounds were tested. Several promising candidates such as S6 were identified. Their activities in buffers, as well as in plasma- and cell lysate-containing solutions were evaluated. We also studied the reaction mechanism of this scavenging process. Finally, the combination of the diselenide catalyst and photosensitizers was used to achieve light-induced H2 S removal. These Se-based scavengers can be useful tools for understanding H2 S/ROS regulations.

Searching for Novel Sources of Hydrogen Sulfide Donors: Chemical Profiling of Polycarpa aurata Extract and Evaluation of the Anti-Inflammatory Effects

Hydrogen sulfide (H2S) is a signaling molecule endogenously produced within mammals' cells that plays an important role in inflammation, exerting anti-inflammatory effects. In this view, the research has shown a growing interest in identifying natural H2S donors. Herein, for the first time, the potential of marine extract as a source of H2S-releasing agents has been explored. Different fractions obtained by the Indonesian ascidian Polycarpa aurata were evaluated for their ability to release H2S in solution. The main components of the most active fraction were then characterized by liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and NMR spectroscopy. The ability of this fraction to release H2S was evaluated in a cell-free assay and J774 macrophages by a fluorimetric method, and its anti-inflammatory activity was evaluated in vitro and in vivo by using carrageenan-induced mouse paw edema. The anti-inflammatory effects were assessed by inhibiting the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX2), and interleukin-6 (IL-6), coupled with a reduction in nitric oxide (NO) and IL-6 levels. Thus, this study defines the first example of a marine source able to inhibit inflammatory responses in vivo through the release of H2S.

An ROS-Responsive Donor That Self-Reports Its H2S Delivery by Forming a Benzoxazole-Based Fluorophore

Hydrogen sulfide (H2S), an endogenous signaling molecule, is known to play a pivotal role in neuroprotection, vasodilation, and hormonal regulation. To further explore the biological effects of H2S, refined donors that facilitate its biological delivery, especially under specific (patho) physiological conditions, are needed. In the present study, we demonstrate that ortho-substituted, aryl boronate esters provide two unique and distinct pathways for H2S release from thioamide-based donors: Lewis acid-facilitated hydrolysis and reactive oxygen species (ROS)-induced oxidation/cyclization. Through a detailed structure-activity relationship study, donors that resist hydrolysis and release H2S solely via the latter mechanism were identified, which have the added benefit of providing a potentially useful heterocycle as the lone byproduct of this novel chemistry. To highlight this, we developed an ROS-activated donor (QH642) that simultaneously synthesizes a benzoxazole-based fluorophore en route to its H2S delivery. A distinct advantage of this design over earlier self-reporting donors is that fluorophore formation is possible only if H2S has been discharged from the donor. This key feature eliminates the potential for false positives and provides a more accurate depiction of reaction progress and donor delivery of H2S, including in complex cellular environments.

Advances and Opportunities in H2S Measurement in Chemical Biology

Hydrogen sulfide (H2S) is an important biological mediator across all kingdoms of life and plays intertwined roles in various disciplines, ranging from geochemical cycles to industrial processes. A common need across these broad disciplines is the ability to detect and measure H2S in complex sample environments. This Perspective focuses on key advances and opportunities for H2S detection and quantification that are relevant to chemical biology. Specifically, we focus on methods for H2S detection and quantification most commonly used in biological samples, including activity-based H2S probes, the methylene blue assay, the monobromobimane assay, and H2S-sensitive electrode measurements. Our goal is to help simplify what at first may seem to be an overwhelming array of detection and measurement choices, to articulate the strengths and limitations of individual techniques, and to highlight key unmet needs and opportunities in the field.

Hydrogen sulfide: Recent development of its dual donors and hybrid drugs

Hydrogen sulfide (H2 S) is an important gaseous signalling molecule known to be critically involved in regulating cellular redox homeostasis. As the beneficial and therapeutic effects of H2 S in pathophysiology, such as in cardiovascular and neurodegenerative diseases, have emerged, so too has the drive for the development of H2 S-releasing compounds (aka donors) and their therapeutic applications. Most reported donor compounds singularly release H2 S through biocompatible triggers. An emerging area in the field is the development of compounds that can co-deliver H2 S with other drugs or biologically relevant species, such as reactive oxygen and nitrogen species (ROS and RNS, respectively). These H2 S-based dual donors and hybrid drugs are expected to offset negative side effects from individual treatments or achieve synergistic effects rendering them more clinically effective. Additionally, considering that molecules exist and interact physiologically, dual donors may more accurately mimic biological systems as compared to single donors and allow for the elucidation of fundamental chemistry and biology. This review focuses on the recent advances in the development of H2 S-based dual donors and hybrid drugs along with their design principles and synergistic effects.

Direct hydrogen selenide (H2Se) release from activatable selenocarbamates

Hydrogen selenide (H₂Se) is a possible bioregulator, potential gasotransmitter, and important precursor in biological organoselenium compound synthesis. Early tools for H₂Se research have benefitted from available mechanistic understanding of analogous small molecules developed for detecting or delivering H₂S. A now common approach for H₂S delivery is the use of small molecule thiocarbamates that can be engineered to release COS, which is quickly converted to H₂S by carbonic anhydrase. To expand our understanding of the chemical underpinnings that enable H₂Se delivery, we investigated whether selenocarbamates undergo similar chemistry to release carbonyl selenide (COSe). Using both light- and hydrolysis-activated systems, we demonstrate that unlike their lighter thiocarbamate congeners, selenocarbamates release H₂Se directly with concomitant isocyanate formation rather than by the intermediate release of COSe. This reaction mechanism for direct H₂Se release is further supported by computational investigations that identify a ΔΔG^‡ ∼ 25 kcal mol^-1 between the H₂Se and COSe release pathways in the absence of protic solvent. This work highlights fundamentally new approaches for H₂Se release from small molecules and advances the understanding of reactivity differences between reactive sulfur and selenium species.

Characterization of Glutathione Dithiophosphates as Long-Acting H2S Donors

Considering the important cytoprotective and signaling roles but relatively narrow therapeutic index of hydrogen sulfide (H₂S), advanced H₂S donors are required to achieve a therapeutic effect. In this study, we proposed glutathione dithiophosphates as new combination donors of H₂S and glutathione. The kinetics of H₂S formation in dithiophosphate solutions suggested a continuous H₂S release by the donors, which was higher for the dithiophosphate of reduced glutathione than oxidized glutathione. The compounds, unlike NaHS, inhibited the proliferation of C2C12 myoblasts at submillimolar concentrations due to an efficient increase in intracellular H₂S. The H₂S donors more profoundly affected reactive oxygen species and reduced glutathione levels in C2C12 myocytes, in which these parameters were elevated compared to myoblasts. Oxidized glutathione dithiophosphate as well as control donors exerted antioxidant action toward myocytes, whereas the effect of reduced glutathione dithiophosphate at (sub-)micromolar concentrations was rather modulating. This dithiophosphate showed an enhanced negative inotropic effect mediated by H₂S upon contraction of the atrial myocardium, furthermore, its activity was prolonged and reluctant for washing. These findings identify glutathione dithiophosphates as redox-modulating H₂S donors with long-acting profile, which are of interest for further pharmacological investigation.

New Insights into Oxidative and Reductive Stress Responses and Their Relation to the Anticancer Activity of Selenium-Containing Compounds as Hydrogen Selenide Donors

Redox balance is important for the homeostasis of normal cells, but also for the proliferation, progression, and survival of cancer cells. Both oxidative and reductive stress can be harmful to cells. In contrast to oxidative stress, reductive stress and the therapeutic opportunities underlying the mechanisms of reductive stress in cancer, as well as how cancer cells respond to reductive stress, have received little attention and are not as well characterized. Therefore, there is recent interest in understanding how selective induction of reductive stress may influence therapeutic treatment and disease progression in cancer. There is also the question of how cancer cells respond to reductive stress. Selenium compounds have been shown to have chemotherapeutic effects against cancer, and their anticancer mechanism is thought to be related to the formation of their metabolites, including hydrogen selenide (H₂Se), which is a highly reactive and reducing molecule. Here, we highlight recent reports on the molecular mechanism of how cells recognize and respond to oxidative and reductive stress (1) and the mechanisms through which different types of selenium compounds can generate H₂Se (2) and thus selectively affect reductive stress under controlled conditions, which may be important for their anticancer effects.

Prodrugs of sulfide and persulfide species: Implications in their different pharmacological activities

Reactive sulfur species (RSS), such as H₂S, hydrogen polysulfide (H₂S_n, n ≥ 2), and hydropersulfides (RSS_nH, n ≥ 1), are known to mediate diverse signaling pathways and possess a plethora of exciting therapeutic opportunities. Historically, due to the rapid inter-conversion among those species in vivo, the biological differences of distinct sulfur species were often overlooked. These species were considered to enrich the global sulfur pool in almost an equal fashion. However, advancement in this field has revealed that sulfur species at different oxidation states result in different pharmacological effects including scavenging reactive oxygen species (ROS), activating ion channels, and exhibiting analgesic effects. Here, we summarize recent advances in studying the biological and pharmacological differences of distinct sulfur species; discuss this phenomenon from the view of chemical properties and sulfur signaling pathways; and lay out a roadmap to transforming such new knowledge into general principles in developing sulfur-based therapeutics.

Enzyme-Triggered Chemodynamic Therapy via a Peptide-H2 S Donor Conjugate with Complexed Fe2

Inducing high levels of reactive oxygen species (ROS) inside tumor cells is a cancer therapy method termed chemodynamic therapy (CDT). Relying on delivery of Fenton reaction promoters such as Fe2+ , CDT takes advantage of overproduced ROS in the tumor microenvironment. We developed a peptide-H2 S donor conjugate, complexed with Fe2+ , termed AAN-PTC-Fe2+ . The AAN tripeptide was specifically cleaved by legumain, an enzyme overexpressed in glioma cells, to release carbonyl sulfide (COS). Hydrolysis of COS by carbonic anhydrase formed H2 S, an inhibitor of catalase, an enzyme that detoxifies H2 O2 . Fe2+ and H2 S together increased intracellular ROS levels and decreased viability in C6 glioma cells compared with controls lacking either Fe2+ , the AAN sequence, or the ability to generate H2 S. AAN-PTC-Fe2+ performed better than temezolimide while exhibiting no cytotoxicity toward H9C2 cardiomyocytes. This study provides an H2 S-amplified, enzyme-responsive platform for synergistic cancer treatment.

The Rhodanese PspE Converts Thiosulfate to Cellular Sulfane Sulfur in Escherichia coli

Hydrogen sulfide (H₂S) and its oxidation product zero-valent sulfur (S⁰) play important roles in animals, plants, and bacteria. Inside cells, S⁰ exists in various forms, including polysulfide and persulfide, which are collectively referred to as sulfane sulfur. Due to the known health benefits, the donors of H₂S and sulfane sulfur have been developed and tested. Among them, thiosulfate is a known H₂S and sulfane sulfur donor. We have previously reported that thiosulfate is an effective sulfane sulfur donor in Escherichia coli; however, it is unclear how it converts thiosulfate to cellular sulfane sulfur. In this study, we showed that one of the various rhodaneses, PspE, in E. coli was responsible for the conversion. After the thiosulfate addition, the ΔpspE mutant did not increase cellular sulfane sulfur, but the wild type and the complemented strain ΔpspE::pspE increased cellular sulfane sulfur from about 92 μM to 220 μM and 355 μM, respectively. LC-MS analysis revealed a significant increase in glutathione persulfide (GSSH) in the wild type and the ΔpspE::pspE strain. The kinetic analysis supported that PspE was the most effective rhodanese in E. coli in converting thiosulfate to glutathione persulfide. The increased cellular sulfane sulfur alleviated the toxicity of hydrogen peroxide during E. coli growth. Although cellular thiols might reduce the increased cellular sulfane sulfur to H₂S, increased H₂S was not detected in the wild type. The finding that rhodanese is required to convert thiosulfate to cellular sulfane sulfur in E. coli may guide the use of thiosulfate as the donor of H₂S and sulfane sulfur in human and animal tests.

Insights into self-degradation of cysteine esters and amides under physiological conditions yield new cleavable chemistry

An unprecedented H₂S release from cysteine esters and amides (CysO/NHR) under physiological conditions was discovered and the plausible mechanism was proposed. Alkylation of the amino moiety of cysteine esters enables the H₂S release to be tuned and further provides support to the mechanistic insights. This discovery not only provides new insights into several fundamental science issues including non-enzymatic H₂S-produced pathways, but also inspires new tunable cleavable motifs for sustained release of arylthiols and even for prodrug design.

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.

A Theranostic Probe for Promotion of Skin Wound Healing by Exudate-Triggered H2S Release with Self-Monitoring Ability

Hydrogen sulfide (H₂S) as an endogenous gasotransmitter plays a critical role in promotion of wound healing. However, the current H₂S release system lacks the in situ monitoring ability, which may lead to insufficient or overdose release of H₂S and serious side effects. Herein, we develop a self-monitoring theranostic probe TPATCF-S, which can quickly release H₂S under water stimuli associated with a self-monitoring ability by a color change from colorless to deep blue. With a full thickness dermal defect as a model, the TPATCF-S absorbed on alginate dressings can be used for wound exudate-responsive release of H₂S to efficiently promote skin wound healing.

N-thiocarboxyanhydrides, amino acid-derived enzyme-activated H2S donors, enhance sperm mitochondrial activity in presence and absence of oxidative stress

BACKGROUND

Hydrogen sulfide (H₂S) donors are crucial tools not only for understanding the role of H₂S in cellular function but also as promising therapeutic agents for oxidative stress-related diseases. This study aimed to explore the effect of amino acid-derived N-thiocarboxyanhydrides (NTAs), which release physiological H₂S levels in the presence of carbonic anhydrase, on porcine sperm function during short-term incubation with and without induced oxidative stress. For this purpose, we employed two H₂S-releasing NTAs with release half-lives (t_1/2) in the range of hours that derived from the amino acids glycine (Gly-NTA) or leucine (Leu-NTA). Because carbonic anhydrase is crucial for H₂S release from NTAs, we first measured the activity of this enzyme in the porcine ejaculate. Then, we tested the effect of Gly- and Leu-NTAs at 10 and 1 nM on sperm mitochondrial activity, plasma membrane integrity, acrosomal status, motility, motile subpopulations, and redox balance during short-term incubation at 38 °C with and without a reactive oxygen species (ROS)-generating system.

RESULTS

Our results show that carbonic anhydrase is found both in spermatozoa and seminal plasma, with activity notably higher in the latter. Both Gly- and Leu-NTAs did not exert any noxious effects, but they enhanced sperm mitochondrial activity in the presence and absence of oxidative stress. Moreover, NTAs (except for Leu-NTA 10 nM) tended to preserve the sperm redox balance against the injuries provoked by oxidative stress, which provide further support to the antioxidant effect of H₂S on sperm function. Both compounds also increased progressive motility over short-term incubation, which may translate into prolonged sperm survival.

CONCLUSIONS

The presence of carbonic anhydrase activity in mammalian spermatozoa makes NTAs promising molecules to investigate the role of H₂S in sperm biology. For the first time, beneficial effects of NTAs on mitochondrial activity have been found in mammalian cells in the presence and absence of oxidative stress. NTAs are interesting compounds to investigate the role of H₂S in sperm mitochondria-dependent events and to develop H₂S-related therapeutic protocols against oxidative stress in assisted reproductive technologies.

Intelligent polymeric hydrogen sulfide delivery systems for therapeutic applications

Hydrogen sulfide (H₂S) plays an important role in regulating various pathological processes such as protecting mammalian cell from harmful injuries, promoting tissue regeneration, and regulating the process of various diseases caused by physiological disorders. Studies have revealed that the physiological effects of H₂S are highly associated with its concentrations. At relatively low concentration, H₂S shows beneficial functions. However, long-time and high-dose donation of H₂S would inhibit regular biological process, resulting in cell dysfunction and apoptosis. To regulate the dosage of H₂S delivery for precision medicine, H₂S delivery systems with intelligent characteristics were developed and a variety of biocompatibility polymers have been utilized to establish intelligent polymeric H₂S delivery systems, with the abilities to specifically target the lesions, smartly respond to pathological microenvironments, as well as real-timely monitor H₂S delivery and lesion conditions by incorporating imaging-capable moieties. In this review, we focus on the design, preparation, and therapeutic applications of intelligent polymeric H₂S delivery systems in cardiovascular therapy, inflammatory therapy, tissue regenerative therapy, cancer therapy and bacteria-associated therapy. Strategies for precise H₂S therapies especially imaging-guided H₂S theranostics are highlighted. Since H₂S donors with stimuli-responsive characters are vital components for establishing intelligent H₂S delivery systems, the development of H₂S donors is also briefly introduced.

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H₂S is an endogenous gasotransmitter that plays important role in regulating various physiological and pathological pathways.

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Controlled H₂S delivery is vital since the therapeutic effects of H₂S are highly associated with its concentrations.

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Intelligent polymeric H₂S delivery systems possess specific targeting, stimuli responsive and imaging guided capabilities, representing a strategic option for next generation of therapies.

Recent development of hydrogen sulfide-releasing biomaterials as novel therapies: a narrative review

Hydrogen sulfide (H₂S) has been reported as an endogenous gasotransmitter that contributes to the modulation of a myriad of biological signalling pathways, which includes maintaining homeostasis in living organisms at physiological concentrations, controlling protein sulfhydration and persulfidation for signalling processes, mediating neurodegeneration, and regulating inflammation and innate immunity, etc. As a result, researchers are actively exploring effective approaches to evaluate the properties and the distribution of H₂S in vivo. Furthermore, the regulation of the physiological conditions of H₂S in vivo introduces the opportunity to further study the molecular mechanisms by which H₂S regulates cellular functions. In recent years, many H₂S-releasing compounds and biomaterials that can deliver H₂S to various body systems have been developed to provide sustained and stable H₂S delivery. Additionally, various designs of these H₂S-releasing biomaterials have been proposed to aid in the normal conduction of physiological processes, such as cardioprotection and wound healing, by modulating different signalling pathways and cell functionalities. Using biomaterials as a platform to control the delivery of H₂S introduces the opportunity to fine tune the physiological concentration of H₂S in vivo, a key to many therapeutic applications. In this review, we highlight recent research works concerning the development and application of H₂S-releasing biomaterials with a special emphasis to different release triggering conditions in in vivo studies. We believe that the further exploration of the molecular mechanisms underlying H₂S donors and their function when incorporated with various biomaterials will potentially help us understand the pathophysiological mechanisms of different diseases and assist the development of H₂S-based therapies.

Enol-mediated delivery of H2Se from γ-keto selenides: mechanistic insight and evaluation

Like hydrogen sulfide (H2S), its chalcogen congener, hydrogen selenide (H2Se), is an emerging molecule of interest given its endogenous expression and purported biological activity. However, unlike H2S, detailed investigations into the chemical biology of H2Se are limited and little is known about its innate physiological functions, cellular targets, and therapeutic potential. The obscurity surrounding these fundamental questions is largely due to a lack of small molecule donors that can effectively increase the bioavailability of H2Se through their continuous liberation of the transient biomolecule under physiologically relevant conditions. Driven by this unmet demand for H2Se-releasing moieties, we report that γ-keto selenides provide a useful platform for H2Se donation via an α-deprotonation/β-elimination pathway that is highly dependent on both pH and alpha proton acidity. These attributes afforded a small library of donors with highly variable rates of release (higher alpha proton acidity = faster selenide liberation), which is accelerated under neutral to slightly basic conditions-a feature that is unique and complimentary to previously reported H2Se donors. We also demonstrate the impressive anticancer activity of γ-keto selenides in both HeLa and HCT116 cells in culture, which is likely to stimulate additional interest and research into the biological activity and anticancer effects of H2Se. Collectively, these results indicate that γ-keto selenides provide a highly versatile and effective framework for H2Se donation.

Hydrogen Sulfide: A Gaseous Mediator and Its Key Role in Programmed Cell Death, Oxidative Stress, Inflammation and Pulmonary Disease

Hydrogen sulfide (H2S) has been acknowledged as a novel gaseous mediator. The metabolism of H2S in mammals is tightly controlled and is mainly achieved by many physiological reactions catalyzed by a suite of enzymes. Although the precise actions of H2S in regulating programmed cell death, oxidative stress and inflammation are yet to be fully understood, it is becoming increasingly clear that H2S is extensively involved in these crucial processes. Since programmed cell death, oxidative stress and inflammation have been demonstrated as three important mechanisms participating in the pathogenesis of various pulmonary diseases, it can be inferred that aberrant H2S metabolism also functions as a critical contributor to pulmonary diseases, which has also been extensively investigated. In the meantime, substantial attention has been paid to developing therapeutic approaches targeting H2S for pulmonary diseases. In this review, we summarize the cutting-edge knowledge on the metabolism of H2S and the relevance of H2S to programmed cell death, oxidative stress and inflammation. We also provide an update on the crucial roles played by H2S in the pathogenesis of several pulmonary diseases. Finally, we discuss the perspective on targeting H2S metabolism in the treatment of pulmonary diseases.

Therapeutic gas-releasing nanomedicines with controlled release: Advances and perspectives

Nanoparticle-based drug delivery has become one of the most popular approaches for maximising drug therapeutic potentials. With the notable improvements, a greater challenge hinges on the formulation of gasotransmitters with unique challenges that are not met in liquid and solid active ingredients. Gas molecules upon release from formulations for therapeutic purposes have not really been discussed extensively. Herein, we take a critical look at four key gasotransmitters, that is, carbon monoxide (CO), nitric oxide (NO), hydrogen sulphide (H2S) and sulphur dioxide (SO2), their possible modification into prodrugs known as gas-releasing molecules (GRMs), and their release from GRMs. Different nanosystems and their mediatory roles for efficient shuttling, targeting and release of these therapeutic gases are also reviewed extensively. This review thoroughly looks at the diverse ways in which these GRM prodrugs in delivery nanosystems are designed to respond to intrinsic and extrinsic stimuli for sustained release. In this review, we seek to provide a succinct summary for the development of therapeutic gases into potent prodrugs that can be adapted in nanomedicine for potential clinical use.

Subcellular Delivery of Hydrogen Sulfide Using Small Molecule Donors Impacts Organelle Stress

Hydrogen sulfide (H₂S) is an endogenously produced gaseous signaling molecule with important roles in regulating organelle function and stress. Because of its high reactivity, targeted delivery of H₂S using small molecule H₂S donors has garnered significant interest to minimize off-target effects. Although mitochondrially targeted H₂S donors, such as AP39, have been reported previously and exhibit significantly higher potency than nontargeted donors, the expansion of targeted H₂S delivery to other subcellular organelles remains largely absent. To fill this key unmet need, we report a library of organelle-targeted H₂S donors that localize H₂S delivery to specific subcellular organelles, including the Golgi apparatus, lysosome, endoplasmic reticulum, and mitochondria. We measured H₂S production in vitro from each donor, confirmed the localization of H₂S delivery using organelle-specific H₂S responsive fluorescent probes, and demonstrated enhanced potency of these targeted H₂S donors in providing protection against organelle-specific stress. We anticipate this class of targeted H₂S donors will enable future studies of subcellular roles of H₂S and the pathways by which H₂S alleviates subcellular organelle stress.

Reactive sulfur and selenium species in the regulation of bone homeostasis

Reactive oxygen species (ROS) are important modulators of physiological signaling and play important roles in bone tissue regulation. Both reactive sulfur species (RSS) and reactive selenium species (RSeS) are involved in ROS signaling, and recent work suggests RSS and RSeS involvement in the regulation of bone homeostasis. For example, RSS can promote osteogenic differentiation and decrease osteoclast activity and differentiation, and the antioxidant activity of RSeS play crucial roles in balancing bone remodeling. Here, we outline current research progress on the application of RSS and RSeS in bone disease and regeneration. Focusing on these investigations, we highlight different methods, tools, and sources of RSS and RSeS, and we also highlight future opportunities for delivery of RSS and RSeS in biological environments relating to bone.

Supramolecular Activation of S8 by Cucurbiturils in Water and Mechanism of Reduction to H2S by Thiols: Insights into Biological Sulfane Sulfur Trafficking

Reactive sulfur species (RSS) play critical roles in diverse chemical environments. Molecules containing sulfane sulfur (S⁰) have emerged as key species involved in cellular redox buffering as well as RSS generation, translocation, and action. Using cucurbit[7]uril (CB[7]) as a model hydrophobic host, we demonstrate here that S₈ can be encapsulated to form a 1:1 host guest complex, which was confirmed by solution state experiments, mass spectrometry, and X-ray crystallography. The solid state structure of CB[7]/S₈ shows that the encapsulated S₈ is available to nucleophiles through the carbonyl portals of the host. Treatment of CB[7]/S₈ with thiols results in efficient reduction of S₈ to H₂S in water at physiological pH. We establish that encapsulated S₈ is attacked by a thiol within the CB[7] host and that the resultant soluble hydropolysulfide is ejected into solution, where it reacts further with thiols to generate soluble sulfane sulfur carriers and ultimately H₂S. The formation of these intermediate is supported by observed kinetic saturation behavior, competitive inhibition experiments, and alkylative trapping experiments. We also demonstrate that CB[7]/S₈ can be used to increase sulfane sulfur levels in live cells using fluorescence microscopy. More broadly, this work suggests a general activation mechanism of S₈ by hydrophobic motifs, which may be applicable to proteins, membranes, or other bimolecular compartments that could transiently bind and solubilize S₈ to promote reaction with thiols to solubilize and shuttle S₈ back into the redox labile sulfane sulfur pool. Such a mechanism would provide an attractive manifold in which to understand the RSS translocation and trafficking.

Progress and perspective on hydrogen sulfide donors and their biomedical applications

Following the discovery of nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H₂ S) has been identified as the third gasotransmitter in humans. Increasing evidence have shown that H₂ S is of preventive or therapeutic effects on diverse pathological complications. As a consequence, it is of great significance to develop suitable approaches of H₂ S-based therapeutics for biomedical applications. H₂ S-releasing agents (H₂ S donors) play important roles in exploring and understanding the physiological functions of H₂ S. More importantly, accumulating studies have validated the theranostic potential of H₂ S donors in extensive repertoires of in vitro and in vivo disease models. Thus, it is imperative to summarize and update the literatures in this field. In this review, first, the background of H₂ S on its chemical and biological aspects is concisely introduced. Second, the studies regarding the H₂ S-releasing compounds are categorized and described, and accordingly, their H₂ S-donating mechanisms, biological applications, and therapeutic values are also comprehensively delineated and discussed. Necessary comparisons between related H₂ S donors are presented, and the drawbacks of many typical H₂ S donors are analyzed and revealed. Finally, several critical challenges encountered in the development of multifunctional H₂ S donors are discussed, and the direction of their future development as well as their biomedical applications is proposed. We expect that this review will reach extensive audiences across multiple disciplines and promote the innovation of H₂ S biomedicine.

Hydrogen Sulfide Biology and Its Role in Cancer

Hydrogen sulfide (H2S) is an endogenous biologically active gas produced in mammalian tissues. It plays a very critical role in many pathophysiological processes in the body. It can be endogenously produced through many enzymes analogous to the cysteine family, while the exogenous source may involve inorganic sulfide salts. H2S has recently been well investigated with regard to the onset of various carcinogenic diseases such as lung, breast, ovaries, colon cancer, and neurodegenerative disorders. H2S is considered an oncogenic gas, and a potential therapeutic target for treating and diagnosing cancers, due to its role in mediating the development of tumorigenesis. Here in this review, an in-detail up-to-date explanation of the potential role of H2S in different malignancies has been reported. The study summarizes the synthesis of H2S, its roles, signaling routes, expressions, and H2S release in various malignancies. Considering the critical importance of this active biological molecule, we believe this review in this esteemed journal will highlight the oncogenic role of H2S in the scientific community.

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

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

Bioresponsive nano-antibacterials for H2S-sensitized hyperthermia and immunomodulation against refractory implant-related infections

There is an increasingly growing demand for nonantibiotic strategies to overcome drug resistance in bacterial biofilm infections. Here, a novel "gas-sensitized hyperthermia" strategy is proposed for appreciable bacteria killing by the smart design of a metal-organic framework (MOF)-sealed Prussian blue-based nanocarrier (MSDG). Once the biofilm microenvironment (BME) is reached, the acidity-activated MOF degradation allows the release of diallyl trisulfide and subsequent glutathione-responsive generation of hydrogen sulfide (H₂S) gas. Upon near-infrared irradiation, H₂S-sensitized hyperthermia arising from MSDG can efficiently eliminate biofilms through H₂S-induced extracellular DNA damage and heat-induced bacterial death. The generated H₂S in the biofilm can stimulate the polarization of macrophages toward M2 phenotype for reshaping immune microenvironment. Subsequently, the secretion of abundant regeneration-related cytokines from M2 macrophages accelerates tissue regeneration by reversing the infection-induced pro-inflammatory environment in an implant-related infection model. Collectively, such BME-responsive nano-antibacterials can achieve biofilm-specific H₂S-sensitized thermal eradiation and immunomodulatory tissue remodeling, thus realizing the renaissance of precision treatment of refractory implant-related infections.

Implantation of injectable SF hydrogel with sustained hydrogen sulfide delivery reduces neuronal pyroptosis and enhances functional recovery after severe intracerebral hemorrhage

Hydrogen sulfide (H₂S), an important endogenous signaling molecule, plays an important neuroprotective role in the central nervous system. However, there is no ideal delivery material or method involving the sustained and controlled release of H₂S for clinical application in brain diseases. Silk fibroin (SF)-based hydrogels have become a potentially promising strategy for local, controlled, sustained drug release in the treatment of various disorders. Here, we show a silk fibroin (SF)-based hydrogel with sustained H₂S delivery (H₂S@SF hydrogel) is effective in treating brain injury through stereotactic orthotopic injection in a severe intracerebral hemorrhage (ICH) mouse model. In this study, we observed H₂S@SF hydrogel sustained H₂S release in vitro and in vivo. The physicochemical properties of H₂S@SF hydrogel were studied using FE-SEM, Raman spectroscopy and Rheological analysis. Treatment with H₂S@SF hydrogel attenuated brain edema, reduced hemorrhage volume and improved the recovery of neurological deficits after severe ICH following stereotactic orthotopic injection. Double immunofluorescent staining also revealed that H₂S@SF hydrogel may reduce cell pyroptosis in the striatum, cortex and hippocampus. However, when using endogenous H₂S production inhibitor AOAA, H₂S@SF hydrogel could not suppress ICH-induced cell pyroptosis. Hence, the therapeutic effect of the H₂S@SF hydrogel may be partly the result of the slow-release of H₂S and/or the effect of the SF hydrogel on the production of endogenous H₂S. Altogether, the results exhibit promising attributes of injectable silk fibroin hydrogel and the utility of H₂S-loaded injectable SF hydrogel as an alternative biomaterial toward brain injury treatment for clinical application.

Cysteine-Activated Small-Molecule H2Se Donors Inspired by Synthetic H2S Donors

The importance of selenium (Se) in biology and health has become increasingly clear. Hydrogen selenide (H₂Se), the biologically available and active form of Se, is suggested to be an emerging nitric oxide (NO)-like signaling molecule. Nevertheless, the research on H₂Se chemical biology has technique difficulties due to the lack of well-characterized and controllable H₂Se donors under physiological conditions, as well as a robust assay for direct H₂Se quantification. Motivated by these needs, here, we demonstrate that selenocyclopropenones and selenoamides are tunable donor motifs that release H₂Se upon reaction with cysteine (Cys) at pH 7.4 and that structural modifications enable the rate of Cys-mediated H₂Se release to be tuned. We monitored the reaction pathways for the H₂Se release and confirmed H₂Se generation qualitatively using different methods. We further developed a quantitative assay for direct H₂Se trapping and quantitation in an aqueous solution, which should also be operative for investigating future H₂Se donor motifs. In addition, we demonstrate that arylselenoamide has the capability of Cys-mediated H₂Se release in cellular environments. Importantly, mechanistic investigations and density functional theory (DFT) calculations illustrate the plausible pathways of Cys-activated H₂Se release from arylselenoamides in detail, which may help understand the mechanistic issues of the H₂S release from pharmacologically important arylthioamides. We anticipate that the well-defined chemistries of Cys-activated H₂Se donor motifs will be useful for studying Se biology and for development of new H₂Se donors and bioconjugate techniques.

Radiolysis Studies of Oxidation and Nitration of Tyrosine and Some Other Biological Targets by Peroxynitrite-Derived Radicals

The widespread interest in free radicals in biology extends far beyond the effects of ionizing radiation, with recent attention largely focusing on reactions of free radicals derived from peroxynitrite (i.e., hydroxyl, nitrogen dioxide, and carbonate radicals). These radicals can easily be generated individually by reactions of radiolytically-produced radicals in aqueous solutions and their reactions can be monitored either in real time or by analysis of products. This review first describes the general principles of selective radical generation by radiolysis, the yields of individual species, the advantages and limitations of either pulsed or continuous radiolysis, and the quantitation of oxidizing power of radicals by electrode potentials. Some key reactions of peroxynitrite-derived radicals with potential biological targets are then discussed, including the characterization of reactions of tyrosine with a model alkoxyl radical, reactions of tyrosyl radicals with nitric oxide, and routes to nitrotyrosine formation. This is followed by a brief outline of studies involving the reactions of peroxynitrite-derived radicals with lipoic acid/dihydrolipoic acid, hydrogen sulphide, and the metal chelator desferrioxamine. For biological diagnostic probes such as ‘spin traps’ to be used with confidence, their reactivities with radical species have to be characterized, and the application of radiolysis methods in this context is also illustrated.

Pyridoxal-5-phosphate induced cardioprotection in aging associated with up-expression of cystathionine-γ-lyase, 3-mercaptopyruvate sulfurtransferase, and ATP-sensitive potassium channels

BACKGROUND

In the present work, we investigated the cardioprotective potential of pyridoxal-5-phosphate (PLP) in old rats as a cofactor of enzymes that synthesize hydrogen sulphide (H₂ S).

MATERIALS AND METHODS

PLP was administered per os in a dose of 0.7 mg per kg daily for 2 weeks. Rats were divided into three groups (adult, old and old +PLP) of 20 animals. The cardiac mRNA levels of genes encoding H₂ S-synthesizing enzymes cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST), uncoupling proteins (UCP3), subunits of ATP-sensitive potassium (K_ATP ) channels were determined using real-time polymerase chain reaction analysis. We also studied the effect of PLP-administration on the content of H₂ S, oxidative stress, the activities of inducible and constitutive NO-synthase (iNOS, cNOS), arginase and nitrate reductase in the heart homogenates as well as cardiac resistance to ischemia-reperfusion in Langendorff-isolated heart model.

RESULTS

It was shown that PLP restored mRNA levels of CSE, 3-MST and UCP3 genes, and H₂ S content and also significantly increased the expression of SUR2 and Kir6.1 (2.2 and 3.3 times, respectively) in the heart of old rats. PLP significantly reduced the formation of superoxide, malondialdehyde, diene conjugates as well as the activity of iNOS and arginase. PLP significantly increased constitutive synthesis of NO and prevented reperfusion disturbances of the heart function after ischemia.

CONCLUSIONS

Thus, PLP-administration in old rats was associated with up-expression of CSE, 3-MST, UCP3 and SUR2 and Kir6.1 subunits of K_ATP channels, and also increased cNOS activity and reduced oxidative stress and prevented reperfusion dysfunction of the heart in ischemia-reperfusion.

Methods for Suppressing Hydrogen Sulfide in Biological Systems

Significance: Hydrogen sulfide (H₂S) plays critical roles in redox biology, and its regulatory effects are tightly controlled by its cellular location and concentration. The imbalance of H₂S is believed to contribute to some pathological processes. Recent Advances: Downregulation of H₂S requires chemical tools such as inhibitors of H₂S-producing enzymes and H₂S scavengers. Recent efforts have discovered some promising inhibitors and scavengers. These advances pave the road toward better understanding of the functions of H₂S. Critical Issues: Precise H₂S downregulation is challenging. The potency and specificity of current inhibitors are still far from ideal. H₂S-producing enzymes are involved in complex sulfur metabolic pathways and ubiquitously present in biological matrices. The inhibition of these enzymes can cause unwanted side effects. H₂S scavengers allow targeted H₂S clearance, but their options are still limited. In addition, the scavenging process often results in biologically active by-products. Future Directions: Further development of potent and specific inhibitors for H₂S-producing enzymes is needed. Scavengers that can rapidly and selectively remove H₂S while generating biocompatible by-products are needed. Potential therapeutic applications of scavengers and inhibitors are worth exploring. Antioxid. Redox Signal. 36, 294-308.

A fluorogenic H2S donor activated by reactive oxygen species for real-time monitoring in cells and in vivo

Hydrogen sulfide (H₂S) is an important gasotransmitter in biological system, and plays a crucial role in varied physiological and pathological processes. Exogenous H₂S is widely employed as a positive control in H₂S related biological study. Herein, we develop a reactive oxygen species (ROS) triggered donor HSD545 that delivers H₂S and simultaneously generates a fluorophore to real-time monitoring the process of H₂S release in vitro and in vivo. The donor exhibits low cytotoxicity and strong cytoprotection against ROS-induce oxidative stress.

Hydrogen sulfide as a therapeutic option for the treatment of Duchenne muscular dystrophy and other muscle-related diseases

Hydrogen sulfide (H₂S) has been known for years as a poisoning gas and until recently evoked mostly negative associations. However, the discovery of its gasotransmitter functions suggested its contribution to various physiological and pathological processes. Although H₂S has been found to exert cytoprotective effects through modulation of antioxidant, anti-inflammatory, anti-apoptotic, and pro-angiogenic responses in a variety of conditions, its role in the pathophysiology of skeletal muscles has not been broadly elucidated so far. The classical example of muscle-related disorders is Duchenne muscular dystrophy (DMD), the most common and severe type of muscular dystrophy. Mutations in the DMD gene that encodes dystrophin, a cytoskeletal protein that protects muscle fibers from contraction-induced damage, lead to prominent dysfunctions in the structure and functions of the skeletal muscle. However, the main cause of death is associated with cardiorespiratory failure, and DMD remains an incurable disease. Taking into account a wide range of physiological functions of H₂S and recent literature data on its possible protective role in DMD, we focused on the description of the 'old' and 'new' functions of H₂S, especially in muscle pathophysiology. Although the number of studies showing its essential regulatory action in dystrophic muscles is still limited, we propose that H₂S-based therapy has the potential to attenuate the progression of DMD and other muscle-related disorders.

Thiobenzophenones: tunable hydrolysis-based donors for intracellular H2S delivery

H2S, the third gasotransmitter, is involved in many physiological and pathological processes. Compounds that can release H2S slowly under physiological conditions are useful chemical tools for studying H2S biology as...

Design and Development of a Bioorthogonal, Visualizable and Mitochondria-Targeted Hydrogen Sulfide (H2 S) Delivery System

Hydrogen sulfide (H₂ S) is an important endogenous gasotransmitter, but the targeted delivery and real-time feedback of exogenous H₂ S are still challenging. With the aid of density functional theory (DFT) calculations, we designed a new 1,3-dithiolium-4-olate (DTO) compound, which can react with a strained alkyne via the 1,3-dipolar cycloaddition and the retro-Diels-Alder reaction to generate carbonyl sulfide (COS) as the precursor of H₂ S, and a thiophene derivative with turn-on fluorescence. Moreover, the diphenylamino substituent in DTO greatly increases the mitochondrial targeting of this H₂ S delivery system. Such a bioorthogonal click-and-release reaction has integrated three functions in one system for the first time: (1) in situ controllable H₂ S release, (2) concomitant fluorescence response, and (3) mitochondria-targeted delivery. In addition, we investigated the mitochondrial membrane potential loss alleviation by using this system in H9c2 cells under oxidative stress.

[Impairments in metabolism of amino acids - precursors of gasotransmitters - in the premature birth]

The content of amino acids - sources of gasotransmitters and the activity of enzymes of their metabolism have been studied in the placenta and amniotic fluid in full-term and complicated by preterm birth (PB). Determination of amino acids was carried out using an automatic analyzer; specific spectrophotometric methods were used to assess the activity of enzymes. The development of PB is accompanied by changes in the amino acid level already in the second trimester of pregnancy. Correlation of differently directions was found between the level of amino acids and the activity of the corresponding enzymes. The imbalance of amino acids in the fetoplacental system in PB is accompanied by a change in the production of their low molecular weight derivatives gas transmitters (NO, CO, H2S), which play an important role in the regulation of numerous metabolic processes.

Moving Past Quinone-Methides: Recent Advances toward Minimizing Electrophilic Byproducts from COS/H2S Donors

Hydrogen sulfide (H2S) is an important biomolecule that plays key signaling and protective roles in different physiological processes. With the goals of advancing both the available research tools and the associated therapeutic potential of H2S, researchers have developed different methods to deliver H2S on-demand in different biological contexts. A recent approach to develop such donors has been to design compounds that release carbonyl sulfide (COS), which is quickly converted to H2S in biological systems by the ubiquitous enzyme carbonic anhydrase (CA). Although highly diversifiable, many approaches using this general platform release quinone methides or related electrophiles after donor activation. Many such electrophiles are likely scavenged by water, but recent efforts have also expanded alternative approaches that minimize the formation of electrophilic byproducts generated after COS release. This mini-review focuses specifically on recent examples of COS-based H2S donors that do not generate quinone methide byproducts after donor activation.

The Hidden Role of Hydrogen Sulfide Metabolism in Cancer

Hydrogen Sulfide (H₂S), an endogenously produced gasotransmitter, is involved in various important physiological and disease conditions, including vasodilation, stimulation of cellular bioenergetics, anti-inflammation, and pro-angiogenesis. In cancer, aberrant up-regulation of H₂S-producing enzymes is frequently observed in different cancer types. The recognition that tumor-derived H₂S plays various roles during cancer development reveals opportunities to target H₂S-mediated signaling pathways in cancer therapy. In this review, we will focus on the mechanism of H₂S-mediated protein persulfidation and the detailed information about the dysregulation of H₂S-producing enzymes and metabolism in different cancer types. We will also provide an update on mechanisms of H₂S-mediated cancer progression and summarize current options to modulate H₂S production for cancer therapy.

N-Methylation of Self-Immolative Thiocarbamates Provides Insights into the Mechanism of Carbonyl Sulfide Release

Hydrogen sulfide (H₂S) is an important biomolecule, and self-immolative thiocarbamates have shown great promise as triggerable H₂S donors with suitable analogous control compounds; however, thiocarbamates with electron-deficient payloads are less efficient H₂S donors. We report here the synthesis and study of a series of N-methylated esterase-triggered thiocarbamates that block the postulated unproductive deprotonation-based pathway for these compounds. The relative reaction profiles for H₂S release across a series of electron-rich and electron-poor N-Me aniline payloads are examined experimentally and computationally. We show that thiocarbamate N-methylation does block some side reactivity and increases the H₂S release profiles for electron-poor donors. Additionally, we show that isothiocyanate release is not a competitive pathway, and rather that the reduced efficiency of electron-poor donors is likely due to other side reactions.

Metal-organic frameworks for therapeutic gas delivery

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S) are gaseous signaling molecules (gasotransmitters) that regulate both physiological and pathological processes and offer therapeutic potential for the treatment of many diseases, such as cancer, cardiovascular disease, renal disease, bacterial and viral infections. However, the inherent labile nature of therapeutic gases results in difficulties in direct gases administration and their controlled delivery at clinically relevant ranges. Metal-organic frameworks (MOFs) with highly porous, stable, and easy-to-tailor properties have shown promising therapeutic gas delivery potential. Herein, we highlight the recent advances of MOF-based platforms for therapeutic gas delivery, either by endogenous (i.e., direct transfer of gases to targets) or exogenous (i.e., stimulating triggered release of gases) means. Reports that involve in vitro and/or in vivo studies are highlighted due to their high potential for clinical translation. Current challenges for clinical requirements and possible future innovative designs to meet variable healthcare needs are discussed.

Sulfur-containing therapeutics in the treatment of Alzheimer's disease

Sulfur is widely existent in natural products and synthetic organic compounds as organosulfur, which are often associated with a multitude of biological activities. OBenzothiazole, in which benzene ring is fused to the 4,5-positions of the thiazolerganosulfur compounds continue to garner increasing amounts of attention in the field of medicinal chemistry, especially in the development of therapeutic agents for Alzheimer's disease (AD). AD is a fatal neurodegenerative disease and the primary cause of age-related dementia posing severe societal and economic burdens. Unfortunately, there is no cure for AD. A lot of research has been conducted on sulfur-containing compounds in the context of AD due to their innate antioxidant potential and some are currently being evaluated in clinical trials. In this review, we have described emerging trends in the field, particularly the concept of multi-targeting and formulation of disease-modifying strategies. SAR, pharmacological targets, in vitro/vivo ADMET, efficacy in AD animal models, and applications in clinical trials of such sulfur compounds have also been discussed. This article provides a comprehensive review of organosulfur-based AD therapeutic agents and provides insights into their future development.

Basic Pharmacological Characterization of EV-34, a New H2S-Releasing Ibuprofen Derivative

BACKGROUND

Cardioprotective effects of H2S are being suggested by numerous studies. Furthermore, H2S plays a role in relaxation of vascular smooth muscle, protects against oxidative stress, and modulates inflammation. Long-term high-dose use of NSAIDs, such as ibuprofen, have been associated with enhanced cardiovascular risk. The goal of the present work is the synthesis and basic pharmacological characterization of a newly designed H2S-releasing ibuprofen derivative.

METHODS

Following the synthesis of EV-34, a new H2S-releasing derivative of ibuprofen, oxidative stability assays were performed (Fenton and porphyrin assays). Furthermore, stability of the molecule was studied in rat serum and liver lysates. H2S-releasing ability of the EC-34 was studied with a hydrogen sulfide sensor. MTT (3-(4,5-dimethylthiazol 2-yl)-2,5-(diphenyltetrazolium bromide)) assay was carried out to monitor the possible cytotoxic effect of the compound. Cyclooxygenase (COX) inhibitory property of EV-34 was also evaluated. Carrageenan assay was carried out to compare the anti-inflammatory effect of EV-34 to ibuprofen in rat paws.

RESULTS

The results revealed that the molecule is stable under oxidative condition of Fenton reaction. However, EV-34 undergoes biodegradation in rat serum and liver lysates. In cell culture medium H2S is being released from EV-34. No cytotoxic effect was observed at concentrations of 10, 100, 500 µM. The COX-1 and COX-2 inhibitory effects of the molecule are comparable to those of ibuprofen. Furthermore, based on the carrageenan assay, EV-34 exhibits the same anti-inflammatory effect to that of equimolar amount of ibuprofen (100 mg/bwkg).

CONCLUSION

The results indicate that EV-34 is a safe H2S releasing ibuprofen derivative bearing anti-inflammatory properties.