Hydrogen sulfide: a gaseous signaling molecule modulates tissue homeostasis: implications in ophthalmic diseases

Glutathione Modulates Hydrogen Sulfide Release and the Ocular Hypotensive Action of Diallyl Polysulfide Compounds

BACKGROUND

Hydrogen sulfide (H2S) is an endogenous transmitter with the potential to regulate aqueous humor dynamics and protect retinal neurons from degeneration. The aim of the present study was two-fold: (a) to evaluate the release of H2S from two polysulfides, diallyl disulfide (DADS), and diallyl trisulfide (DATS); and (b) to investigate their ocular hypotensive actions in normotensive male and female rabbits in the presence and absence of GSH.

MATERIALS AND METHODS

H2S was quantified hourly for up to 6 h using a H2S-Biosensor (World Precision Instruments, Sarasota, Fl). Intraocular pressure (IOP) was assessed in normotensive New Zealand Albino rabbits using a pneumotonometer (model 30 classic; Reichert Ophthalmic Instruments, Depew, NY, USA).

RESULTS

In the presence of GSH, there was an increase in the in vitro release of H2S produced by DADS and DATS. Both DADS and DATS also caused a dose-dependent reduction in IOP in male and female rabbits, in both treated and untreated eyes. For instance, in male animals, the presence of GSH (3% and 5%) significantly (p < 0.05, n = 5) enhanced the ocular hypotensive action of DADS (2%) and DATS (2%) from 14.02 ± 2.89% to 18.67 ± 5.6% and from 16.22 ± 3.48 to 23.62 ± 5.79%, respectively.

CONCLUSIONS

GSH enhanced both H2S release and ocular hypotensive action of the polysulfides in a manner that was dependent on the number of sulfur atoms present in each polysulfide. Furthermore, female animals were less sensitive to the IOP-lowering action of the polysulfides, when compared to their male counterparts.

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

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

Inorganic sulfides prevent osimertinib-induced mitochondrial dysfunction in human iPS cell-derived cardiomyocytes

Despite the widespread recognition of the global concern regarding the onset of cardiovascular diseases in a significant number of patients following cancer treatment, definitive strategies for prevention and treatment remain elusive. In this study, we established systems to evaluate the influence of anti-cancer drugs on the quality control of mitochondria, pivotal for energy metabolism, using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Osimertinib, an epidermal growth factor receptor tyrosine kinase inhibitor used for treatment in lung cancer, reportedly increases the risk of cardiovascular disease. However, its underlying mechanism is largely unknown. Here, we found that the treatment of hiPSC-CMs with osimertinib and doxorubicin, but not trastuzumab and cisplatin, revealed a concentration-dependent impairment of respiratory function accompanied by mitochondrial fission. We previously reported the significant role of sulfur metabolism in maintaining mitochondrial quality in the heart. Co-treatment with various inorganic sulfur donors (Na2S, Na2S2, Na2S3) alongside anti-cancer drugs demonstrated that Na2S attenuated the cardiotoxicity of osimertinib but not doxorubicin. Osimertinib decreased intracellular reduced sulfur levels, while Na2S treatment suppressed the sulfur leakage, suggesting its potential in mitigating osimertinib-induced cardiotoxicity. These results imply the prospect of inorganic sulfides, such as Na2S, as a seed for precision pharmacotherapy to alleviate osimertinib's cardiotoxic effects.

Signaling Paradigms of H2S-Induced Vasodilation: A Comprehensive Review

Hydrogen sulfide (H2S), a gas traditionally considered toxic, is now recognized as a vital endogenous signaling molecule with a complex physiology. This comprehensive study encompasses a systematic literature review that explores the intricate mechanisms underlying H2S-induced vasodilation. The vasodilatory effects of H2S are primarily mediated by activating ATP-sensitive potassium (K_ATP) channels, leading to membrane hyperpolarization and subsequent relaxation of vascular smooth muscle cells (VSMCs). Additionally, H2S inhibits L-type calcium channels, reducing calcium influx and diminishing VSMC contraction. Beyond ion channel modulation, H2S profoundly impacts cyclic nucleotide signaling pathways. It stimulates soluble guanylyl cyclase (sGC), increasing the production of cyclic guanosine monophosphate (cGMP). Elevated cGMP levels activate protein kinase G (PKG), which phosphorylates downstream targets like vasodilator-stimulated phosphoprotein (VASP) and promotes smooth muscle relaxation. The synergy between H2S and nitric oxide (NO) signaling further amplifies vasodilation. H2S enhances NO bioavailability by inhibiting its degradation and stimulating endothelial nitric oxide synthase (eNOS) activity, increasing cGMP levels and potent vasodilatory responses. Protein sulfhydration, a post-translational modification, plays a crucial role in cell signaling. H2S S-sulfurates oxidized cysteine residues, while polysulfides (H2Sn) are responsible for S-sulfurating reduced cysteine residues. Sulfhydration of key proteins like K_ATP channels and sGC enhances their activity, contributing to the overall vasodilatory effect. Furthermore, H2S interaction with endothelium-derived hyperpolarizing factor (EDHF) pathways adds another layer to its vasodilatory mechanism. By enhancing EDHF activity, H2S facilitates the hyperpolarization and relaxation of VSMCs through gap junctions between endothelial cells and VSMCs. Recent findings suggest that H2S can also modulate transient receptor potential (TRP) channels, particularly TRPV4 channels, in endothelial cells. Activating these channels by H2S promotes calcium entry, stimulating the production of vasodilatory agents like NO and prostacyclin, thereby regulating vascular tone. The comprehensive understanding of H2S-induced vasodilation mechanisms highlights its therapeutic potential. The multifaceted approach of H2S in modulating vascular tone presents a promising strategy for developing novel treatments for hypertension, ischemic conditions, and other vascular disorders. The interaction of H2S with ion channels, cyclic nucleotide signaling, NO pathways, ROS (Reactive Oxygen Species) scavenging, protein sulfhydration, and EDHF underscores its complexity and therapeutic relevance. In conclusion, the intricate signaling paradigms of H2S-induced vasodilation offer valuable insights into its physiological role and therapeutic potential, promising innovative approaches for managing various vascular diseases through the modulation of vascular tone.

Esterase-Activated Hydrogen Sulfide Donors with Self-Reporting Fluorescence Properties and Highly Tunable Rates of Delivery

Hydrogen sulfide (H2S) has emerged as a significant biomolecule with diverse activities, akin to other gaseous signaling molecules such as nitric oxide (NO) and carbon monoxide (CO). In the present study, we report on the development of esterase-activated donors that track their direct cellular donation of H2S by enlisting a cyclization reaction onto a thioamide that forms a fluorogenic byproduct. This simple donor design provides a noninvasive method for monitoring the biological delivery and activity of H2S, along with access to a library of compounds with highly variable rates of H2S delivery. These studies culminated with the identification of a slow-release, yet highly efficient, donor (ZL-DMA-Ph) that was shown to self-report its gradual and continuous cellular donation of H2S for up to 24 h which, in addition to better mimicking the natural biosynthesis of H2S, provided impressive cytoprotection in a cellular cardiotoxicity model, even at submicromolar concentrations. In total, these findings indicate that the esterase-triggered fluorogenic donors identified in this study will offer new opportunities for exploring the chemical biology and therapeutic potential of exogenous H2S supplementation.

Hydrogen Sulfide Modulation of Matrix Metalloproteinases and CD147/EMMPRIN: Mechanistic Pathways and Impact on Atherosclerosis Progression

Atherosclerosis is a chronic inflammatory condition marked by endothelial dysfunction, lipid accumulation, inflammatory cell infiltration, and extracellular matrix (ECM) remodeling within arterial walls, leading to plaque formation and potential cardiovascular events. Key players in ECM remodeling and inflammation are matrix metalloproteinases (MMPs) and CD147/EMMPRIN, a cell surface glycoprotein expressed on endothelial cells, vascular smooth muscle cells (VSMCs), and immune cells, that regulates MMP activity. Hydrogen sulfide (H₂S), a gaseous signaling molecule, has emerged as a significant modulator of these processes including oxidative stress mitigation, inflammation reduction, and vascular remodeling. This systematic review investigates the mechanistic pathways through which H₂S influences MMPs and CD147/EMMPRIN and assesses its impact on atherosclerosis progression. A comprehensive literature search was conducted across PubMed, Scopus, and Web of Science databases, focusing on studies examining H₂S modulation of MMPs and CD147/EMMPRIN in atherosclerosis contexts. Findings indicate that H₂S modulates MMP expression and activity through transcriptional regulation and post-translational modifications, including S-sulfhydration. By mitigating oxidative stress, H₂S reduces MMP activation, contributing to plaque stability and vascular remodeling. H₂S also downregulates CD147/EMMPRIN expression via transcriptional pathways, diminishing inflammatory responses and vascular cellular proliferation within plaques. The dual regulatory role of H₂S in inhibiting MMP activity and downregulating CD147 suggests its potential as a therapeutic agent in stabilizing atherosclerotic plaques and mitigating inflammation. Further research is warranted to elucidate the precise molecular mechanisms and to explore H₂S-based therapies for clinical application in atherosclerosis.

Cysteine as an Innovative Biomarker for Kidney Injury

BACKGROUND

Kidney transplantation is a widely used treatment for end-stage kidney disease. Nevertheless, the incidence of acute kidney injury (AKI) in deceased donors poses a potential hazard because it significantly increases the risk of delayed graft function and potentially exerts an influence on the kidney allograft outcome. It is crucial to develop a diagnostic model capable of assessing the existence and severity of AKI in renal grafts. However, no suitable kidney injury markers have been developed thus far.

METHODS

We evaluated the efficacy of the molecular probe NPO-B, which selectively responds to cysteine, as a new diagnostic tool for kidney injury. We used an in vitro model using ischemia/reperfusion injury human kidney-2 cells and an in vivo ischemia/reperfusion injury mouse model. Additionally, cysteine was investigated using urine samples from deceased donors and living donors to assess the applicability of detection techniques to humans.

RESULTS

This study confirmed that the NPO-B probe effectively identified and visualized the severity of kidney injury by detecting cysteine in both in vitro and in vivo models. We observed that the fluorescence intensity of urine samples measured using NPO-B from the deceased donors who are at a high risk of renal injury was significantly stronger than that of the living donors.

CONCLUSIONS

If implemented in clinical practice, this new diagnostic tool using NPO-B can potentially enhance the success rate of kidney transplantation by accurately determining the extent of AKI in renal grafts.

Transdermal Hydrogen Sulfide Delivery Enabled by Open-Metal-Site Metal-Organic Frameworks

Hydrogen sulfide (H2S) is an endogenously produced gasotransmitter involved in many physiological processes that are integral to proper cellular functioning. Due to its profound anti-inflammatory and antioxidant properties, H2S plays important roles in preventing inflammatory skin disorders and improving wound healing. Transdermal H2S delivery is a therapeutically viable option for the management of such disorders. However, current small-molecule H2S donors are not optimally suited for transdermal delivery and typically generate electrophilic byproducts that may lead to undesired toxicity. Here, we demonstrate that H2S release from metal-organic frameworks (MOFs) bearing coordinatively unsaturated metal centers is a promising alternative for controlled transdermal delivery of H2S. Gas sorption measurements and powder X-ray diffraction (PXRD) studies of 11 MOFs support that the Mg-based framework Mg2(dobdc) (dobdc4- = 2,5-dioxidobenzene-1,4-dicarboxylate) is uniquely well-suited for transdermal H2S delivery due to its strong yet reversible binding of H2S, high capacity (14.7 mmol/g at 1 bar and 25 °C), and lack of toxicity. In addition, Rietveld refinement of synchrotron PXRD data from H2S-dosed Mg2(dobdc) supports that the high H2S capacity of this framework arises due to the presence of three distinct binding sites. Last, we demonstrate that transdermal delivery of H2S from Mg2(dobdc) is sustained over a 24 h period through porcine skin. Not only is this significantly longer than sodium sulfide but this represents the first example of controlled transdermal delivery of pure H2S gas. Overall, H2S-loaded Mg2(dobdc) is an easily accessible, solid-state source of H2S, enabling safe storage and transdermal delivery of this therapeutically relevant gas.

Pills of Multi-Target H2S Donating Molecules for Complex Diseases

Among the various drug discovery methods, a very promising modern approach consists in designing multi-target-directed ligands (MTDLs) able to modulate multiple targets of interest, including the pathways where hydrogen sulfide (H2S) is involved. By incorporating an H2S donor moiety into a native drug, researchers have been able to simultaneously target multiple therapeutic pathways, resulting in improved treatment outcomes. This review gives the reader some pills of successful multi-target H2S-donating molecules as worthwhile tools to combat the multifactorial nature of complex disorders, such as inflammatory-based diseases and cancer, as well as cardiovascular, metabolic, and neurodegenerative disorders.

Molecular hydrogen promotes retinal vascular regeneration and attenuates neovascularization and neuroglial dysfunction in oxygen-induced retinopathy mice

BACKGROUND

Retinopathy of Prematurity (ROP) is a proliferative retinal vascular disease occurring in the retina of premature infants and is the main cause of childhood blindness. Nowadays anti-VEGF and retinal photocoagulation are mainstream treatments for ROP, but they develop a variety of complications. Hydrogen (H2) is widely considered as a useful neuroprotective and antioxidative therapeutic method for hypoxic-ischemic disease without toxic effects. However, whether H2 provides physiological angiogenesis promotion, neovascularization suppression and glial protection in the progression of ROP is largely unknown.This study aims to investigate the effects of H2 on retinal angiogenesis, neovascularization and neuroglial dysfunction in the retinas of oxygen-induced retinopathy (OIR) mice.

METHODS

In this study, mice that were seven days old and either wild-type (WT) or Nrf2-deficient (Nrf2-/-) were exposed to 75% oxygen for 5 days and then returned to normal air conditions. Different stages of hydrogen gas (H2) inhalation were administered. Vascular obliteration, neovascularization, and blood vessel leakage were analyzed and compared. To count the number of neovascularization endothelial nuclei, routine HE staining of retinal sections was conducted. Immunohistochemistry was performed using DyLight 594 labeled GSL I-isolectin B4 (IB4), as well as primary antibodies against proliferating cell nuclear antigen (PCNA), glial fibrillary acidic protein (GFAP), and Iba-1. Western blots were used to measure the expression of NF-E2-related factor 2 (Nrf2), vascular endothelial growth factor (VEGF), Notch1, Dll4, and HIF-1α. Additionally, the expression of target genes such as NQO1, HO-1, Notch1, Hey1, Hey2, and Dll4 was measured. Human umbilical vein endothelial cells (HUVECs) treated with H2 under hypoxia were used as an in vitro model. RT-PCR was used to evaluate the mRNA expression of Nrf2, Notch/Dll4, and the target genes. The expression of reactive oxygen species (ROS) was observed using immunofluorescence staining.

RESULTS

Our results indicate that 3-4% H2 does not disturb retinal physiological angiogenesis, but ameliorates vaso-obliteration and neovascularization in OIR mice. Moreover, H2 prevents the decreased density and reverses the morphologic and functional changes in retinal astrocytes caused by oxygen-induced injury. In addition, H2 inhalation reduces microglial activation, especially in the area of neovascularization in OIR mice. H2 plays a protective role in vascular regeneration by promoting Nrf2 activation and suppressing the Dll4-induced Notch signaling pathway in vivo. Also, H2 promotes the proliferation of HUVECs under hypoxia by negatively regulating the Dll4/Notch pathway and reducing ROS levels through Nrf2 pathway aligning with our findings in vivo.Moreover, the retinal oxygen-sensing mechanisms (HIF-1α/VEGF) are also involved in hydrogen-mediated retinal revascularization and neovascularization suppression.

CONCLUSIONS

Collectively, our results indicate that H2 could be a promising therapeutic agent for POR treatment and that its beneficial effect in human ROP might involve the activation of the Nrf2-Notch axis as well as HIF-1α/VEGF pathways.

Biomimetic Vesicles with Designer Phospholipids Can Sense Environmental Redox Cues

Cell-like materials that sense environmental cues can serve as next-generation biosensors and help advance the understanding of intercellular communication. Currently, bottom-up engineering of protocell models from molecular building blocks remains a grand challenge chemists face. Herein, we describe giant unilamellar vesicles (GUVs) with biomimetic lipid membranes capable of sensing environmental redox cues. The GUVs employ activity-based sensing through designer phospholipids that are fluorescently activated in response to specific reductive (hydrogen sulfide) or oxidative (hydrogen peroxide) conditions. These synthetic phospholipids are derived from 1,2-dipalmitoyl-rac-glycero-3-phosphocholine and they possess a headgroup with heterocyclic aromatic motifs. Despite their structural deviation from the phosphocholine headgroup, the designer phospholipids (0.5-1.0 mol %) mixed with natural lipids can vesiculate, and the resulting GUVs (7-20 μm in diameter) remain intact over the course of redox sensing. All-atom molecular dynamics simulations gave insight into how these lipids are positioned within the hydrophobic core of the membrane bilayer and at the membrane-water interface. This work provides a purely chemical method to investigate potential redox signaling and opens up new design opportunities for soft materials that mimic protocells.

Benserazide, a cystathionine beta-synthase (CBS) inhibitor, potentially enhances the anticancer effects of paclitaxel via inhibiting the S-sulfhydration of SIRT1 and the HIF1-α/VEGF pathway

Cancer targeted therapy is essential to minimize damage to normal cells and improve treatment outcomes. The elevated activity of Cystathionine beta-synthase (CBS), an enzyme responsible for producing endogenous hydrogen sulfide (H2S), plays a significant role in promoting tumor growth, invasiveness, and metastatic potential. Consequently, the selective inhibition of CBS could represent a promising therapeutic strategy for cancer. Currently, there is much interest in combining paclitaxel with other drugs for cancer treatment. This study aimed to investigate the efficacy of combining benserazide, a CBS inhibitor, with paclitaxel in treating tumors. Firstly, we demonstrated CBS is indeed involved in the progression of multiple cancers. Then it was observed that the total binding free energy between the protein and the small molecule is -98.241 kJ/mol. The release of H2S in the group treated with 100 μM benserazide was reduced by approximately 90% compared to the negative control, and the thermal denaturation curve of the complex protein shifted to the right, suggesting that benserazide binds to and blocks the CBS protein. Next, it was found that compared to paclitaxel monotherapy, the combination of benserazide with paclitaxel demonstrated stronger antitumor activity in KYSE450, A549, and HCT8 cells, accompanied by reduced cell viability, cell migration and invasion, as well as diminished angiogenic and lymphangiogenic capabilities. In vivo studies showed that the combined administration of benserazide and paclitaxel significantly reduced the volume and weight of axillary lymph nodes in comparison to the control group and single administration group. Further mechanistic studies revealed that the combination of benserazide and paclitaxel significantly suppressed the S-sulfhydration of SIRT1 protein, thereby inhibiting the expression of SIRT1 protein and activating SIRT1 downstream Notch1/Hes1 signaling pathway in KYSE450, A549, and HCT8 cells. Meanwhile, we observed that benserazide combined with paclitaxel induced a more significant downregulation of HIF-1α, VEGF-A, VEGF-C, and VEGF-D proteins expression levels in KYSE450, A549, and HCT8 cells compared to paclitaxel alone. These findings indicated that benserazide enhances the anticancer effects of paclitaxel via inhibiting the S-sulfhydration of SIRT1 and down-regulating HIF-1α/VEGF signaling pathway. This study suggests that benserazide may have potential as a chemosensitizer in cancer treatment.

Development and application of LC-MS/MS method for the quantification of hydrogen sulfide in the eye

There are limited studies that report the physiological levels of H2S in the eye. The currently available UV/Vis methods lack the required sensitivity and precision. Hence, the purpose of this study was to develop and validate a sensitive and robust pre-column derivatization LC-MS/MS method to measure changes in H2S levels in tissues from isolated porcine eyes. H2S was derivatized and an LC-MS/MS method was developed to monitor the derivatized product, Sulfide-dibimane (Sdb) using a reverse phase Waters Acquity BEH C18 column (1.7 μm, 2.1 × 100 mm). H2S quantification was performed using multiple-ion reaction monitoring (MRM) in positive mode, with the transitions of m/z 415.0 → m/z 223.0 for Sdb and m/z 353.0 → m/z 285.0 for internal standard (griseofulvin). This method provided a suitable way to quantify H2S and was then successfully adapted to measure H2S levels in isolated porcine iris-ciliary body tissues previously treated in the presence or absence of varying concentrations of lipopolysaccharide (LPS, 5-100 ng/ml), a pro-inflammatory agent. Isolated iris-ciliary bodies (ICB) from porcine eyes were cut into quadrants of approximately 50 mg and homogenized using a 1:3 volume of homogenizing buffer. H2S in the supernatant was then derivatized with monobromobimane and quantified.

Mechanisms Underlying the Hydrogen Sulfide Actions: Target Molecules and Downstream Signaling Pathways

Significance: As a new important gas signaling molecule like nitric oxide (NO) and carbon dioxide (CO), hydrogen sulfide (H2S), which can be produced by endogenous H2S-producing enzymes through l-cysteine metabolism in mammalian cells, has attracted wide attention for long. H2S has been proved to play an important regulatory role in numerous physiological and pathophysiological processes. However, the deep mechanisms of those different functions of H2S still remain uncertain. A better understanding of the mechanisms can help us develop novel therapeutic strategies. Recent Advances: H2S can play a regulating role through various mechanisms, such as regulating epigenetic modification, protein expression levels, protein activity, protein localization, redox microenvironment, and interaction with other gas signaling molecules such as NO and CO. In addition to discussing the molecular mechanisms of H2S from the above perspectives, this article will review the regulation of H2S on common signaling pathways in the cells, including the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), mitogen-activated protein kinase (MAPK), Janus kinase (JAK)/signal transducer, and activator of transcription (STAT) signaling pathway. Critical Issues: Although there are many studies on the mechanism of H2S, little is known about its direct target molecules. This article will also review the existing reports about them. Furthermore, the interaction between direct target molecules of H2S and the downstream signaling pathways involved also needs to be clarified. Future Directions: An in-depth discussion of the mechanism of H2S and the direct target molecules will help us achieving a deeper understanding of the physiological and pathophysiological processes regulated by H2S, and lay a foundation for developing new clinical therapeutic drugs in the future. Innovation: This review focuses on the regulation of H2S on signaling pathways and the direct target molecules of H2S. We also provide details on the underlying mechanisms of H2S functions from the following aspects: epigenetic modification, regulation of protein expression levels, protein activity, protein localization, redox microenvironment, and interaction with other gas signaling molecules such as NO and CO. Further study of the mechanisms underlying H2S will help us better understand the physiological and pathophysiological processes it regulates, and help develop new clinical therapeutic drugs in the future. Antioxid. Redox Signal. 40, 86-109.

Mechanistic Intimate Insights into the Role of Hydrogen Sulfide in Alzheimer's Disease: A Recent Systematic Review

In the rapidly evolving field of Alzheimer's Disease (AD) research, the intricate role of Hydrogen Sulfide (H2S) has garnered critical attention for its diverse involvement in both pathological substrates and prospective therapeutic paradigms. While conventional pathophysiological models of AD have primarily emphasized the significance of amyloid-beta (Aβ) deposition and tau protein hyperphosphorylation, this targeted systematic review meticulously aggregates and rigorously appraises seminal contributions from the past year elucidating the complex mechanisms of H2S in AD pathogenesis. Current scholarly literature accentuates H2S's dual role, delineating its regulatory functions in critical cellular processes-such as neurotransmission, inflammation, and oxidative stress homeostasis-while concurrently highlighting its disruptive impact on quintessential AD biomarkers. Moreover, this review illuminates the nuanced mechanistic intimate interactions of H2S in cerebrovascular and cardiovascular pathology associated with AD, thereby exploring avant-garde therapeutic modalities, including sulfurous mineral water inhalations and mud therapy. By emphasizing the potential for therapeutic modulation of H2S via both donors and inhibitors, this review accentuates the imperative for future research endeavors to deepen our understanding, thereby potentially advancing novel diagnostic and therapeutic strategies in AD.

Biocompatible 7-nitro-2,1,3-benzoxadiazole-embedded naphthalimide for exploring endogenous H2S in living cells

Hydrogen sulfide (H₂S) is a central signaling and antioxidant biomolecule involved in various biological processes. As inappropriate levels of H₂S in the human body are closely related to various diseases, including cancer, a tool capable of detecting H₂S with high selectivity and sensitivity in living systems is urgently required. In this work, we intended to develop a biocompatible and activatable fluorescent molecular probe for detecting H₂S generation in living cells. The 7-nitro-2,1,3-benzoxadiazole-imbedded naphthalimide (1) probe presented here responds specifically to H₂S and produces readily detectable fluorescence at 530 nm. Interestingly, probe 1 exhibited significant fluorescence responses to changes in endogenous H₂S levels as well as high biocompatibility and permeability in living HeLa cells. This allowed for the real-time monitoring of endogenous H₂S generation as an antioxidant defense response in the oxidatively stressed cells.

Role of 3-Mercaptopyruvate Sulfurtransferase (3-MST) in Physiology and Disease

3-mercaptopyruvate sulfurtransferase (3-MST) plays the important role of producing hydrogen sulfide. Conserved from bacteria to Mammalia, this enzyme is localized in mitochondria as well as the cytoplasm. 3-MST mediates the reaction of 3-mercaptopyruvate with dihydrolipoic acid and thioredoxin to produce hydrogen sulfide. Hydrogen sulfide is also produced through cystathionine beta-synthase and cystathionine gamma-lyase, along with 3-MST, and is known to alleviate a variety of illnesses such as cancer, heart disease, and neurological conditions. The importance of cystathionine beta-synthase and cystathionine gamma-lyase in hydrogen sulfide biogenesis is well-described, but documentation of the 3-MST pathway is limited. This account compiles the current state of knowledge about the role of 3-MST in physiology and pathology. Attempts at targeting the 3-MST pathway for therapeutic benefit are discussed, highlighting the potential of 3-MST as a therapeutic target.

HPLC Study of Product Formed in the Reaction of NBD-Derived Fluorescent Probe with Hydrogen Sulfide, Cysteine, N-acetylcysteine, and Glutathione

Hydrogen sulfide (H₂S) and its bioderivatives analogs, such as L-cysteine (L-Cys) and glutathione (GSH), are ubiquitous biological thiols in the physiological and pathological processes of living systems. Their aberrant concentration levels are associated with many diseases. Although several NBD-based fluorescence probes have been developed to detect biological thiols, the HPLC-detection of H₂S, GSH, L-Cys, and N-acetylcysteine-specific products has not been described. Herein, a novel NBD-derived pro-coumarin probe has been synthesized and used to develop a new strategy for the triple mode detection of H₂S and such thiols as GSH, L-Cys, and NAC. Hydrogen sulfide and those biothiols at physiological pH release fluorescent coumarin from the probe and cause a significant fluorescence enhancement at 473 nm. The appropriate NBD-derived product for H₂S, L-Cys, GSH, and NAC has a different color and retention time that allows distinguishing these biological thiols meaning the probe has a great possibility in the biological application. Fluorescent imaging combined with colorimetric and HPLC detection of H₂S/biothiol-specific product(s) brings a potential tool for confirming the presence of biological thiols and determining concentrations in various aqueous biological samples.

Bamboo Salt and Triple Therapy Synergistically Inhibit Helicobacter pylori-Induced Gastritis In Vivo: A Preliminary Study

Helicobacter pylori infections are a major cause of gastrointestinal disorders, including gastric ulcers, gastritis, and gastric cancer. Triple therapy, using two antibiotics and a proton pump inhibitor, is recommended for the treatment of H. pylori infections. However, antibiotic resistance in H. pylori is an emerging issue. Bamboo salt, a traditional Korean salt made by baking solar sea salt in bamboo barrels, can ameliorate the symptoms of various gastrointestinal diseases. Herein, we compared the anti-H. pylori activity of triple therapy (clarithromycin, metronidazole, and omeprazole), solar salt, and bamboo salt in vivo as a preliminary study. Four-week-old C57BL/6 male mice were inoculated for eight weeks with the H. pylori Sydney Strain 1 (SS-1) and orally administered triple therapy drugs and salts for five days. The transcript levels of the H. pylori-expressed gene CagA and inflammatory cytokines Tnfα and Il-1β significantly decreased in the bamboo salt treated mice than those in the H. pylori-infected control group. This effect was further enhanced by using triple therapy and bamboo salt together. Solar salt caused modest inhibition of H. pylori-induced inflammation. We also demonstrated the synergistic effects of bamboo salt and triple therapy against H. pylori. Thus, bamboo salt may be a potential candidate agent against the treatment of H. pylori-associated gastritis.

Design, Synthesis and Evaluation of Novel Molecular Hybrids between Antiglaucoma Drugs and H2S Donors

Glaucoma is a group of eye diseases consisting of optic nerve damage with corresponding loss of field vision and blindness. Hydrogen sulfide (H₂S) is a gaseous neurotransmitter implicated in various pathophysiological processes. It is involved in the pathological mechanism of glaucomatous neuropathy and exerts promising effects in the treatment of this disease. In this work, we designed and synthetized new molecular hybrids between antiglaucoma drugs and H₂S donors to combine the pharmacological effect of both moieties, providing a heightened therapy. Brinzolamide, betaxolol and brimonidine were linked to different H₂S donors. The H₂S-releasing properties of the new compounds were evaluated in a phosphate buffer solution by the amperometric approach, and evaluated in human primary corneal epithelial cells (HCEs) by spectrofluorometric measurements. Experimental data showed that compounds 1c, 1d and 3d were the hybrids with the best properties, characterized by a significant and long-lasting production of the gasotransmitter both in the aqueous solution (in the presence of L-cysteine) and in the intracellular environment. Because, to date, the donation of H₂S by antiglaucoma H₂S donor hybrids using non-immortalized corneal cells has never been reported, these results pave the way to further investigation of the potential efficacy of the newly synthesized compounds.

Function of gaseous hydrogen sulfide in liver fibrosis

Over the past few years, hydrogen sulfide (H₂S) has been shown to exert several biological functions in mammalian. The endogenous production of H₂S is mainly mediated by cystathione β-synthase, cystathione γ-lyase and 3-mercaptopyruvate sulfur transferase. These enzymes are broadly expressed in liver tissue and regulates liver function by working on a variety of molecular targets. As an important regulator of liver function, H₂S is critically involved in the pathogenesis of various liver diseases, such as non-alcoholic steatohepatitis and liver cancer. Targeting H₂S-generating enzymes may be a therapeutic strategy for controlling liver diseases. This review described the function of H₂S in liver disease and summarized recent characterized role of H₂S in several cellular process of the liver.

Ratiometric Detection of H2S in Liver Injury by Activated Two-Wavelength Photoacoustic Imaging

Metformin is commonly used for clinical treatment of type-2 diabetes, but long-term or overdose intake of metformin usually causes selective upregulation of H₂S level in the liver, resulting in liver injury. Therefore, tracking the changes of H₂S content in the liver would contribute to the prevention and diagnosis of liver injury. However, in the literature, there are few reports on ratiometric PA molecular probes for H₂S detection in drug-induced liver injury (DILI). Accordingly, here we developed a H₂S-activated ratiometric PA probe, namely BDP-H₂S, based Aza-BODIPY dye for detecting the H₂S upregulation of metformin-induced liver injury. Due to the intramolecular charge transfer (ICT) effect, BDP-H₂S exhibited a strong PA signal at 770 nm. Following the response to H₂S, its ICT effect was recovered which showed a decrement of PA₇₇₀ and an enhancement of PA₈₄₀. The ratiometric PA signal (PA₈₄₀/PA₇₇₀) showed excellent H₂S selectivity response with a low limit of detection (0.59 μM). Bioimaging experiments demonstrated that the probe has been successfully used for ratiometric PA imaging of H₂S in cells and metformin-induced liver injury in mice. Overall, the designed probe emerges as a powerful tool for noninvasive and accurate imaging of H₂S level and tracking its distribution and variation in liver in-real time.

Design of Intelligent Diagnosis and Treatment System for Ophthalmic Diseases Based on Deep Neural Network Model

Artificial intelligence (AI) has developed rapidly in the field of ophthalmology. Fundus images have become a research hotspot because they are easy to obtain and rich in biological information. The application of fundus image analysis (AI) in background image analysis has been deepened and expanded. At present, a variety of AI studies have been carried out in the clinical screening, diagnosis, and prognosis of eye diseases, and the research results have been gradually applied to clinical practice. The application of AI in fundus image analysis will improve the situation of lack of medical resources and low diagnosis efficiency. In the future, the research of AI eye images should focus on the comprehensive intelligent diagnosis of various ophthalmic diseases and complex diseases. The focus is to integrate standardized and high-quality data resources, improve algorithm efficiency, and formulate corresponding clinical research plans.

Recent Advances in Molecular Research on Hydrogen Sulfide (H2S) Role in Diabetes Mellitus (DM)-A Systematic Review

Abundant experimental data suggest that hydrogen sulfide (H₂S) is related to the pathophysiology of Diabetes Mellitus (DM). Multiple molecular mechanisms, including receptors, membrane ion channels, signalingmolecules, enzymes, and transcription factors, are known to be responsible for the H₂S biological actions; however, H₂S is not fully documented as a gaseous signaling molecule interfering with DM and vascular-linked pathology. In recent decades, multiple approaches regarding therapeutic exploitation of H₂S have been identified, either based on H₂S exogenous apport or on its modulated endogenous biosynthesis. This paper aims to synthesize and systematize, as comprehensively as possible, the recent literature-related data regarding the therapeutic/rehabilitative role of H₂S in DM. This review was conducted following the “Preferred reporting items for systematic reviews and meta-analyses” (PRISMA) methodology, interrogating five international medically renowned databases by specific keyword combinations/“syntaxes” used contextually, over the last five years (2017–2021). The respective search/filtered and selection methodology we applied has identified, in the first step, 212 articles. After deploying the next specific quest steps, 51 unique published papers qualified for minute analysis resulted. To these bibliographic resources obtained through the PRISMA methodology, in order to have the best available information coverage, we added 86 papers that were freely found by a direct internet search. Finally, we selected for a connected meta-analysis eight relevant reports that included 1237 human subjects elicited from clinical trial registration platforms. Numerous H₂S releasing/stimulating compounds have been produced, some being used in experimental models. However, very few of them were further advanced in clinical studies, indicating that the development of H₂S as a therapeutic agent is still at the beginning.

Inhalative as well as Intravenous Administration of H2S Provides Neuroprotection after Ischemia and Reperfusion Injury in the Rats' Retina

BACKGROUND

Neuronal ischemia-reperfusion injury (IRI), such as it can occur in glaucoma or strokes, is associated with neuronal cell death and irreversible loss of function of the affected tissue. Hydrogen sulfide (H2S) is considered a potentially neuroprotective substance, but the most effective route of application and the underlying mechanism remain to be determined.

METHODS

Ischemia-reperfusion injury was induced in rats by a temporary increase in intraocular pressure (1 h). H2S was then applied by inhalation (80 ppm at 0, 1.5, and 3 h after reperfusion) or by intravenous administration of the slow-releasing H2S donor GYY 4137. After 24 h, the retinas were harvested for Western blotting, qPCR, and immunohistochemical staining. Retinal ganglion cell survival was evaluated 7 days after ischemia.

RESULTS

Both inhalative and intravenously delivered H2S reduced retinal ganglion cell death with a better result from inhalative application. H2S inhalation for 1.5 h, as well as GYY 4137 treatment, increased p38 phosphorylation. Both forms of application enhanced the extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, and inhalation showed a significant increase at all three time points. H2S treatment also reduced apoptotic and inflammatory markers, such as caspase-3, intracellular adhesion molecule 1 (ICAM-1), vascular endothelial growth factor (VEGF), and inducible nitric oxide synthase (iNOS). The protective effect of H2S was partly abolished by the ERK1/2 inhibitor PD98059. Inhalative H2S also reduced the heat shock response including heme oxygenase (HO-1) and heat shock protein 70 (HSP-70) and the expression of radical scavengers such as superoxide dismutases (SOD1, SOD2) and catalase.

CONCLUSION

Hydrogen sulfide acts, at least in part, via the mitogen-activated protein kinase (MAPK) ERK1/2 to reduce apoptosis and inflammation. Both inhalative H2S and intravenous GYY 4137 administrations can improve neuronal cell survival.

SM22α-lineage niche cells regulate intramembranous bone regeneration via PDGFRβ-triggered hydrogen sulfide production

Bone stromal cells are critical for bone homeostasis and regeneration. Growing evidence suggests that non-stem bone niche cells support bone homeostasis and regeneration via paracrine mechanisms, which remain to be elucidated. Here, we show that physiologically quiescent SM22α-lineage stromal cells expand after bone injury to regulate diverse processes of intramembranous bone regeneration. The majority of SM22α-lineage cells neither act as stem cells in vivo nor show their expression patterns. Dysfunction of SM22α-lineage niche cells induced by loss of platelet-derived growth factor receptor β (PDGFRβ) impairs bone repair. We further show that PDGFRβ-triggered hydrogen sulfide (H₂S) generation in SM22α-lineage niche cells facilitates osteogenesis and angiogenesis and suppresses overactive osteoclastogenesis. Collectively, these data demonstrate that non-stem SM22α-lineage niche cells support the niche for bone regeneration with a PDGFRβ/H₂S-dependent regulatory mechanism. Our findings provide further insight into non-stem bone stromal niche cell populations and niche-regulation strategy for bone repair.

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.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Altered transsulfuration pathway enzymes and redox homeostasis in inherited retinal degenerative diseases

Retinal degenerative diseases result from apoptotic photoreceptor cell death. As endogenously produced gaseous molecules such as hydrogen sulfide (H₂S) and nitric oxide (NO) play a key role in apoptosis, we compared the expression levels of genes and proteins involved in the production of these molecules in the retina of normal dogs and three canine models (rcd1, crd2, and xlpra2) of human inherited retinal degeneration (IRD). Using qRT-PCR, Western blot, and immunohistochemistry (IHC), we showed that mRNA and protein levels of cystathionine β-synthase (CBS), an enzyme that produces H₂S in neurons, are increased in retinal degeneration, but those of cystathionine γ-lyase (CSE), an enzyme involved in the production of glutathione (GSH), an antioxidant, are not. Such findings suggest that increased levels of H₂S that are not counterbalanced by increased antioxidant potential may contribute to disease in affected retinas. We also studied the expression of neuronal and inducible nitric oxide synthase (nNOS and iNOS), the enzymes responsible for NO production. Western blot and IHC results revealed increased levels of nNOS and iNOS, resulting in increased NO levels in mutant retinas. Finally, photoreceptors are rich in polyunsaturated fatty acids (PUFAs) that can make these cells vulnerable to oxidative damage through reactive oxygen species (ROS). Our results showed increased levels of acrolein and hydroxynonenal (4HNE), two main toxic products of PUFAs, surrounding the membranes of photoreceptors in affected canines. Increased levels of these toxic products, together with increased NO and ROS, likely render these cells susceptible to an intrinsic apoptotic pathway involving mitochondrial membranes. To assess this possibility, we measured the levels of BCL2, an anti-apoptotic protein in the mitochondrial membrane. Western blot results showed decreased levels of BCL2 protein in affected retinas. Overall, the results of this study identify alterations in the expression of enzymes directly involved in maintaining the normal redox status of the retina during retinal degeneration, thereby supporting future studies to investigate the role of H₂S and NO in retinal degeneration and apoptosis.

Masked Amino Trimethyl Lock (H2 N-TML) Systems: New Molecular Entities for the Development of Turn-On Fluorophores and Their Application in Hydrogen Sulfide (H2 S) Imaging in Human Cells

Masked trimethyl lock (TML) systems as molecular moieties enabling the bioresponsive release of compounds or dyes in a controlled temporal and spatial manner have been widely applied for the development of drug conjugates, prodrugs or molecular imaging tools. Herein, we report the development of a novel amino trimethyl lock (H2 N-TML) system as an auto-immolative molecular entity for the release of fluorophores. We designed Cou-TML-N3 and MURh-TML-N3 , two azide-masked turn-on fluorophores. The latter was demonstrated to selectively release fluorescent MURh in the presence of physiological concentrations of the redox-signaling molecule H2 S in vitro and was successfully applied to image H2 S in human cells.

Exogenous administration of hydrogen sulfide alleviates homocysteine induced inflammation in ARPE-19 cells

Plasma homocysteine (Hcy) is an independent risk factor for Age related macular degeneration (AMD) and an inducer of inflammation. Homocysteine catabolism releases hydrogen sulfide (H₂S). H₂S has controversial effects on inflammation. In this study we have analysed the endogenous and exogenous H₂S in modulating inflammation using adult retinal pigment epithelial (ARPE-19) cells as an in vitro model for AMD. ARPE-19 cells were treated with various concentrations of Hcy (15, 30 and 50 μM) for 3 h. Expression of Hcy transulfuration genes (CBS, CSE) by qPCR and western blot. H₂S levels were measured using Free Radical Analyzer System (WPI, USA). The inflammatory markers (IL-6 and IL-8) were evaluated using real-time PCR and ELISA. Hcy exposure increased CBS protein expression, hydrogen sulfide levels and pro-inflammatory cytokines, modulating CBS by silencing did not alter H₂S levels, but inhibition of CSE with PAG inhibited H₂S production and decreased cytokine (IL-6 and IL-8) levels. On the contrary exogenous supply of hydrogen sulfide with NaHS and by compound 1c showed anti-inflammatory effects even in the presence of Hcy. This study shows that exogenous delivery of H₂S decreases inflammation in retinal pigment epithelial cells on exposure to Hcy in ARPE-19 cells.

Exogenous H2 S prevents the nuclear translocation of PDC-E1 and inhibits vascular smooth muscle cell proliferation in the diabetic state

Hydrogen sulphide (H₂S) inhibits vascular smooth muscle cell (VSMC) proliferation induced by hyperglycaemia and hyperlipidaemia; however, the mechanisms are unclear. Here, we observed lower H₂S levels and higher expression of the proliferation‐related proteins PCNA and cyclin D1 in db/db mouse aortae and vascular smooth muscle cells treated with 40 mmol/L glucose and 500 μmol/L palmitate, whereas exogenous H₂S decreased PCNA and cyclin D1 expression. The nuclear translocation of mitochondrial pyruvate dehydrogenase complex‐E1 (PDC‐E1) was significantly increased in VSMCs treated with high glucose and palmitate, and it increased the level of acetyl‐CoA and histone acetylation (H3K9Ac). Exogenous H₂S inhibited PDC‐E1 translocation from the mitochondria to the nucleus because PDC‐E1 was modified by S‐sulfhydration. In addition, PDC‐E1 was mutated at Cys101. Overexpression of PDC‐E1 mutated at Cys101 increased histone acetylation (H3K9Ac) and VSMC proliferation. Based on these findings, H₂S regulated PDC‐E1 S‐sulfhydration at Cys101 to prevent its translocation from the mitochondria to the nucleus and to inhibit VSMC proliferation under diabetic conditions.

NO, CO and H2S based pharmaceuticals in the mission of vision (eye health): a comprehensive review

A set of well defined signaling molecules responsible for normal functioning of human physiology including nitric oxide along with carbon monoxide and hydrogen sulphide are referred as “gasotransmitters”. Due to their involvement in almost every system of a human body, the care of highly sensitive organs using these molecules as drugs represents highly fascinating area of research. In connection with these interesting aspects, the applied aspects of these gaseous molecules in maintaining healthy eye and vision have been targeted in this review. Several examples of eye-droppers including NORMs like latanoprost and nipradiol, CORMs like CORM-3 and CORM-A1, and Hydrogen sulfide releasing system like GYY4137 have been discussed in this context. Therefore the relation of these trio-gasotransmitters with the ophthalmic homeostasis on one hand, and de-infecting role on the other hand has been mainly highlighted. Some molecular systems capable of mimicking gasotransmitter action have also been introduced in connection with the titled theme.

Emerging medical therapies in crush syndrome - progress report from basic sciences and potential future avenues

Crush injury is a disease that is commonly found in victims of earthquakes, debris flows, mine disasters, explosions, terrorist attacks, local wars, and other accidents. The complications that arise due to the crush injury inflicted on victims give rise to crush syndrome (CS). If not treated in time, the mortality rate of CS is very high. The most important measure that can be taken to reduce mortality in such situations is to immediately start treatment. However, the traditional treatment methods such as fluid resuscitation, diuresis, and hemodialysis are not feasible enough to be carried out at the disaster scene. So there is a need for developing new treatments that are efficient and convenient. Because it is difficult to diagnose in the disaster area and reach the treatment equipment and treat on time. It has become a new research needs to be directed into identifying new medical treatment targets and methods using the etiology and pathophysiological mechanisms of CS. In recent years, a large number of new anti-oxidant and anti-inflammatory drug therapies have been shown to be highly efficacious in CS rat/mouse models. Some of them are expected to become specific drugs for the emergency treatment of a large number of patients who may develop CS in the aftermath of earthquakes, wars, and other disasters in the future. Hence, we have reviewed the latest research on the medical therapy of CS as a source for anyone wishing to pursue research in this direction.

Current Perspective of Hydrogen Sulfide as a Novel Gaseous Modulator of Oxidative Stress in Glaucoma

Glaucoma is a group of diseases characterized by the progressive loss of retinal ganglion cells and their axons. Elevated intraocular pressure (IOP) is the main clinical manifestation of glaucoma. Despite being in the focus of the studies for decades, the characteristic and the exact pathology of neurodegeneration in glaucoma remains unclear. Oxidative stress is believed to be one of the main risk factors in neurodegeneration, especially its damage to the retinal ganglion cells. Hydrogen sulfide (H₂S), the recently recognized gas signaling molecule, plays a pivotal role in the nervous system, vascular system, and immune system. It has also shown properties in regulating oxidative stress through different pathways in vivo. In this review, we summarize the distribution and the properties of H₂S within the eye with an emphasis on its role in modulating oxidative stress in glaucoma.

Investigating Different Forms of Hydrogen Sulfide in Cerebrospinal Fluid of Various Neurological Disorders

Over the past 30 years a considerable amount of data has accumulated on the multifaceted role of hydrogen sulfide (H₂S) in the central nervous system. Depending on its concentrations, H₂S has opposite actions, ranging from neuromodulator to neurotoxic. Nowadays, accurate determination of H₂S is still an important challenge to understand its biochemistry and functions. In this perspective, this study aims to explore H₂S levels in cerebrospinal fluid (CSF), key biofluid for neurological studies, and to assess alleged correlations with neuroinflammatory and neurodegenerative mechanisms. A validated analytical determination combining selective electrochemical detection with ion chromatography was developed to measure free and bound sulfur forms of H₂S. A first cohort of CSF samples (n = 134) was analyzed from patients with inflammatory and demyelinating disorders (acute disseminated encephalomyelitis; multiple sclerosis), chronic neurodegenerative diseases (Alzheimer disease; Parkinson disease), and motor neuron disease (Amyotrophic lateral sclerosis). Given its analytical features, the chromatographic method resulted sensitive, reproducible and robust. We also explored low molecular weight-proteome linked to sulphydration by proteomics analysis on matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). This study is a first clinical report on CSF H₂S concentrations from neurological diseases and opens up new perspectives on the potential clinical relevance of H₂S and its potential therapeutic application.

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

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

Hydrogen sulfide is synthesized endogenously in both retinal artery and retina mostly via CSE

Hydrogen sulfide (H₂S) is an important gasotransmitter expressed in various tissues of the organism, including the eye. It is known that H₂S is localized especially in the retina and corneal layers in bovine eye. The enzymes that mediate H₂S synthesis are 3-mercaptopyruvate sulfurtransferase (3-MST), cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). Herein, we aimed to investigate the concentration levels and distribution profiles of these enzymes in bovine retina and retinal artery. Enzyme levels were measured by ELISA and distribution were determined by immunofluorescence microscopic analysis. Much higher concentrations of CBS and CSE have been detected in the retinal artery compared to the retina. In both tissues, particulary 3-MST was found at the lowest level while, CSE was determined to be the most abundant enzyme among the others. CBS distribution was shown in both endothelial and smooth muscle layers, while CSE was seen especially in the endothelial layer of the retinal artery. In the retina, CBS and CSE were expressed in cone-basil cells and retinal ganglion cells, while CSE was also present in bipolar cells. Our results indicated that H₂S is synthesized endogenously in ocular tissues. The widespread expression of H₂S synthesizing enzymes in the retina and retinal artery of the bovine eye, which has anatomical similarities with the human eye, may suggest a protective role for H₂S against retinal vascular diseases as well as a regulatory role in the retinal vascular tone.

Short-term ex-vivo exposure to hydrogen sulfide enhances murine hematopoietic stem and progenitor cell migration, homing, and proliferation

For successful transplantation of Hematopoietic Stem cells (HSCs), it is quite necessary that efficient homing, engraftment and retention of HSC self-renewal capacity takes place, which is often restricted due to inadequate number of adult HSCs. Here, we report that short-term ex-vivo treatment of mouse bone marrow mononuclear cells (BMMNCs) to Sodium Hydrogen Sulfide (NaHS, hydrogen sulfide-H2S donor) can be used as a possible strategy to overcome such hurdle. H2S increases the expression of CXCR4 on HSPCs, enhancing their migration toward SDF-1α in-vitro and thus homing to BM niche. . Additionally, in-vitro studies revealed that H2S has a role in activating mitochondria, thus, pushing quiescent HSCs into division. These results suggest a readily available and cost-effective method to facilitate efficient HSC transplantation.

The vital role for nitric oxide in intraocular pressure homeostasis

Catalyzed by endothelial nitric oxide (NO) synthase (eNOS) activity, NO is a gaseous signaling molecule maintaining endothelial and cardiovascular homeostasis. Principally, NO regulates the contractility of vascular smooth muscle cells and permeability of endothelial cells in response to either biochemical or biomechanical cues. In the conventional outflow pathway of the eye, the smooth muscle-like trabecular meshwork (TM) cells and Schlemm's canal (SC) endothelium control aqueous humor outflow resistance, and therefore intraocular pressure (IOP). The mechanisms by which outflow resistance is regulated are complicated, but NO appears to be a key player as enhancement or inhibition of NO signaling dramatically affects outflow function; and polymorphisms in NOS3, the gene that encodes eNOS modifies the relation between various environmental exposures and glaucoma. Based upon a comprehensive review of past foundational studies, we present a model whereby NO controls a feedback signaling loop in the conventional outflow pathway that is sensitive to changes in IOP and its oscillations. Thus, upon IOP elevation, the outflow pathway tissues distend, and the SC lumen narrows resulting in increased SC endothelial shear stress and stretch. In response, SC cells upregulate the production of NO, relaxing neighboring TM cells and increasing permeability of SC's inner wall. These IOP-dependent changes in the outflow pathway tissues reduce the resistance to aqueous humor drainage and lower IOP, which, in turn, diminishes the biomechanical signaling on SC. Similar to cardiovascular pathogenesis, dysregulation of the eNOS/NO system leads to dysfunctional outflow regulation and ocular hypertension, eventually resulting in primary open-angle glaucoma.

Crescent-Shaped Supramolecular Tetrapeptide Nanostructures

Self-assembly of amphiphilic peptide-based building blocks gives rise to a plethora of interesting nanostructures such as ribbons, fibers, and tubes. However, it remains a great challenge to employ peptide self-assembly to directly produce nanostructures with lower symmetry than these highly symmetric motifs. We report here our discovery that persistent and regular crescent nanostructures with a diameter of 28 ± 3 nm formed from a series of tetrapeptides with the general structure AdKSKSEX (Ad = adamantyl group, KS = lysine residue functionalized with an S-aroylthiooxime (SATO) group, E = glutamic acid residue, and X = variable amino acid residue). In the presence of cysteine, the biological signaling gas hydrogen sulfide (H2S) was released from the SATO units of the crescent nanostructures, termed peptide-H2S donor conjugates (PHDCs), reducing levels of reactive oxygen species (ROS) in macrophage cells. Additional in vitro studies showed that the crescent nanostructures alleviated cytotoxicity induced by phorbol 12-myristate-13-acetate more effectively than common H2S donors and a PHDC of a similar chemical structure, AdKSKSE, that formed short nanoworms instead of nanocrescents. Cell internalization studies indicated that nanocrescent-forming PHDCs were more effective in reducing ROS levels in macrophages because they entered into and remained in cells better than nanoworms, highlighting how nanostructure morphology can affect bioactivity in drug delivery.

Characterization of hydrogen sulfide toxicity to human corneal stromal fibroblasts

Hydrogen sulfide gas (H2 S) is a chemical weapon and a common environmental pollutant. H2 S intoxication is lethal to humans and animals. H2 S contact to the eye can cause vision loss. However, the molecular mechanisms associated with H2 S toxicity to the cornea remain unclear, and no specific therapy exists to mitigate ocular damage from H2 S. Here, we report H2 S-induced cytotoxicity and the parameters contributing to the molecular mechanisms associated with corneal toxicity using primary human corneal stromal fibroblasts (hCSFs) in vitro. Sodium hydrosulfide (NaSH) was used as a source of H2 S, and the cytotoxicity of H2 S was determined by treating hCSF cells with varying concentrations of NaSH (0-10 mM) for 0-72 hours. Changes in cell proliferation, oxidative stress factors, and the expression of inflammatory and fibrotic genes were studied using standard commercial kits and qRT-PCR. NaSH exposure to hCSFs showed dose- and time-dependent cytotoxicity. The IC50 of NaSH was determined to be 5.35 mM. NaSH 5.35 mM exposure led to significantly decreased cytochrome c oxidase activity, increased ROS production, and increased expression of inflammatory and fibrotic genes in hCSF cells. H2 S/NaSH exposure alters normal mitochondrial function, oxidative stress, and inflammatory and fibrotic gene responses in corneal stromal fibroblasts in vitro.

A natural cyanobacterial protein C-phycoerythrin as an HS- selective optical probe in aqueous systems

A naturally fluorescent cyanobacterial protein C-phycoerythrin (CPE) was investigated as a fluorescent probe for biologically and environmentally important hydrosulphide (HS^-) ion. It was selective for HS amongst a large anion screen and the optical response was rapid. Sequential UV-visible titration showed considerable peak shift and attenuation with increasing [HS^-] while fluorescence titration proved that HS^- quenched CPE fluorescence in a concentration dependent manner. The linear response range was 0-2 mM HS^- while the Stern Volmer curve was non-linear and the limit of detection was 185.12 μM. Except bicarbonate and glycine, no anion or biomolecule interfered with the detection even at 10 times the concentration of HS^-. It was also free of influences from other sulphur forms like sulphite, sulphate and thiosulphate. CPE reliably detected HS^- in freshwater and effluent samples, though some under- and over - estimation was evident. The % recovery ranged from ~96 to 105% (RSD ~ 0.035-0.188%). FTIR analysis showed significant changes in the amide I and II regions of CPE, along with minor modifications in the amide III region as well, showing that HS^- was able to influence the protein secondary structure at higher concentrations.

Alleviating Cellular Oxidative Stress through Treatment with Superoxide-Triggered Persulfide Prodrugs

Overproduction of superoxide anion (O2.- ), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O2.- to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H2 S). Termed SOPD-NAC, this persulfide donor reacts specifically with O2.- , decomposing to generate N-acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self-assembling peptide (Bz-CFFE-NH2 ) to make a superoxide-responsive, persulfide-donating peptide (SOPD-Pep). Both SOPD-NAC and SOPD-Pep delivered persulfides/H2 S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD-Pep mitigated toxicity induced by phorbol 12-myristate 13-acetate (PMA) more effectively than SOPD-NAC and several control compounds, including common H2 S donors.

Peptide Nanostructure-Mediated Antibiotic Delivery by Exploiting H2S-Rich Environment in Clinically Relevant Bacterial Cultures

Stimuli-responsive self-destructing soft structures serve as versatile hosts for the encapsulation of guest molecules. A new paradigm for H₂S-responsive structures, based on a modified tripeptide construct, is presented along with microscopy evidence of its time-dependent rupture. As a medicinally interesting application, we employed these commercial antibiotic-loaded soft structures for successful drug release and inhibition of clinically relevant, drug-susceptible, and methicillin-resistant Staphylococcus aureus.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.