Hydrogen sulphide-releasing diclofenac derivatives inhibit breast cancer-induced osteoclastogenesis in vitro and prevent osteolysis ex vivo

Inflammatory-stimuli-responsive turn-on NIR fluorogenic theranostic prodrug: adjuvant delivery of diclofenac and hydrogen sulfide attenuates acute inflammatory disorders

Prolonged use of very commonly prescribed non-steroidal anti-inflammatory drugs (NSAIDs) is often associated with undesired side effects, including gastrointestinal ulcers due to the non-selective inhibition of cyclooxygenases. We describe the development of an inflammatory-stimuli-responsive turn-on fluorogenic theranostic prodrug DCF-HS for adjuvant drug delivery. Upon activation by reactive oxygen species (ROS), the prodrug releases diclofenac DCF (active drug) and the NIR fluorophore DCI-NH2 along with carbonyl sulfide (COS). The second activation of COS by the enzyme carbonic anhydrase (CA) generates hydrogen sulfide (H2S). The prodrug was conveniently synthesized using multi-step organic synthesis. The UV-Vis and fluorescence studies revealed the selective reactivity of DCF-HS towards ROS such as H2O2 in the aqueous phase and the desired uncaging of the drug DCF with turn-on NIR fluorescent reporter under physiological conditions. Furthermore, the release of fluorophore DCI-NH2 and drug DCF was confirmed using the reverse phase HPLC method. Compatibility of prodrug activation was studied next in the cellular medium. The prodrug DCF-HS was non-toxic in a representative cancer cell line (HeLa) and a macrophage cell line (RAW 264.7) up to 100 μM concentration, indicating its biocompatibility. The intracellular ROS-mediated activation of the prodrug with the release of NIR dye DCI-NH2 and H2S was investigated in HeLa cells using the H2S-selective probe WSP2. The anti-inflammatory activity of the active drug DCF from the prodrug DCF-HS was studied in the lipopolysaccharide (LPS)-induced macrophage cell line and compared to that of the parent drug DCF using western blot analysis and it was found that the active drug resulted in pronounced inhibition of COX-2 in a dose-dependent manner. Finally, the anti-inflammatory potential of the prodrug and the turn-on fluorescence were validated in the inflammation-induced Wister rat models.

Garlic extract enhances bioceramic bone scaffolds through upregulating ALP & BGLAP expression in hMSC-monocyte co-culture

Bone homeostasis is predicated by osteoblast and osteoclast cell cycles where gene expressions are responsible for their differentiation from human mesenchymal stem cells (hMSC) and monocytes, respectively. The pro-osteogenic potential of an hMSC-monocyte co-culture can be measured through complementary DNA (mRNA synthesis) within the nucleus, known as quantitative polymerase chain reaction (qPCR). Through this technique, the effects of garlic extract (allicin) release from calcium phosphate bone scaffolds on gene expression of bone forming and bone remodeling cells was explored. Results show this complex biomaterial system enhances hMSC differentiation through the upregulation of bone-forming proteins. Osteoblastic gene markers alkaline phosphatase (ALP) and osteocalcin (BGLAP), are respectively upregulated by 3-fold and 1.6-fold by day 14. These mature osteoblasts then upregulate the receptor activator of nuclear factor-kB ligand (RANKL) which recruits osteoclast cells, as captured by a nearly 2-fold higher osteoclast expression of tartrate-resistance acid-phosphatase (ACP5). This also activates antagonist osteoprotegerin (OPG) expression in osteoblasts, decreasing osteoclast resorption potential and ACP5 expression by day 21. The pro-osteogenic environment with garlic extract release is further quantified by a 4× increase in phosphatase activity and visibly captured in immunofluorescent tagged confocal images. Also corroborated by enhanced collagen formation in a preliminary in vivo rat distal femur model, this work collectively reveals how garlic extract can enhance bioceramic scaffolds for bone tissue regenerative applications.

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: An Emerging Precision Strategy for Gas Therapy

Advances in nanotechnology have enabled the rapid development of stimuli-responsive therapeutic nanomaterials for precision gas therapy. Hydrogen sulfide (H₂ S) is a significant gaseous signaling molecule with intrinsic biochemical properties, which exerts its various physiological effects under both normal and pathological conditions. Various nanomaterials with H₂ S-responsive properties, as new-generation therapeutic agents, are explored to guide therapeutic behaviors in biological milieu. The cross disciplinary of H₂ S is an emerging scientific hotspot that studies the chemical properties, biological mechanisms, and therapeutic effects of H₂ S. This review summarizes the state-of-art research on H₂ S-related nanomedicines. In particular, recent advances in H₂ S therapeutics for cancer, such as H₂ S-mediated gas therapy and H₂ S-related synergistic therapies (combined with chemotherapy, photodynamic therapy, photothermal therapy, and chemodynamic therapy) are highlighted. Versatile imaging techniques for real-time monitoring H₂ S during biological diagnosis are reviewed. Finally, the biosafety issues, current challenges, and potential possibilities in the evolution of H₂ S-based therapy that facilitate clinical translation to patients are discussed.

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.

NSAIDs: Old Acquaintance in the Pipeline for Cancer Treatment and Prevention─Structural Modulation, Mechanisms of Action, and Bright Future

The limitations of current chemotherapeutic drugs are still a major issue in cancer treatment. Thus, targeted multimodal therapeutic approaches need to be strategically developed to successfully control tumor growth and prevent metastatic burden. Inflammation has long been recognized as a hallmark of cancer and plays a key role in the tumorigenesis and progression of the disease. Several epidemiological, clinical, and preclinical studies have shown that traditional nonsteroidal anti-inflammatory drugs (NSAIDs) exhibit anticancer activities. This Perspective reports the most recent outcomes for the treatment and prevention of different types of cancers for several NSAIDs alone or in combination with current chemotherapeutic drugs. Furthermore, an extensive review of the most promising structural modifications is reported, such as phospho, H₂S, and NO releasing-, selenium-, metal complex-, and natural product-NSAIDs, among others. We also provide a perspective about the new strategies used to obtain more efficient NSAID- or NSAID derivative- formulations for targeted delivery.

Role of Hydrogen Sulfide in Myocardial Ischemia-Reperfusion Injury

ABSTRACT

Hydrogen sulfide (H2S), generally known as a new gas signal molecule after nitric oxide and carbon monoxide, has been found as an important endogenous gasotransmitter in the last few decades, and it plays a significant role in the cardiovascular system both pathologically and physiologically. In recent years, there is growing evidence that H2S provides myocardial protection against myocardial ischemia-reperfusion injury (MIRI), which resulted in an ongoing focus on the possible mechanisms of action accounting for the H2S cardioprotective effect. At present, lots of mechanisms of action have been verified through in vitro and in vivo models of I/R injury, such as S-sulfhydrated modification, antiapoptosis, effects on microRNA, bidirectional effect on autophagy, antioxidant stress, or interaction with NO and CO. With advances in understanding of the molecular pathogenesis of MIRI and pharmacology studies, the design, the development, and the pharmacological characterization of H2S donor drugs have made great important progress. This review summarizes the latest research progress on the role of H2S in MIRI, systematically explains the molecular mechanism of H2S affecting MIRI, and provides a new idea for the formulation of a myocardial protection strategy in the future.

Ex vivo Bone Models and Their Potential in Preclinical Evaluation

PURPOSE OF REVIEW

Novel therapies for damaged and diseased bone are being developed in a preclinical testing process consisting of in vitro cell experiments followed by in vivo animal studies. The in vitro results are often not representative of the results observed in vivo. This could be caused by the complexity of the natural bone environment that is missing in vitro. Ex vivo bone explant cultures provide a model in which cells are preserved in their native three-dimensional environment. Herein, it is aimed to review the current status of bone explant culture models in relation to their potential in complementing the preclinical evaluation process with specific attention paid to the incorporation of mechanical loading within ex vivo culture systems.

RECENT FINDINGS

Bone explant cultures are often performed with physiologically less relevant bone, immature bone, and explants derived from rodents, which complicates translatability into clinical practice. Mature bone explants encounter difficulties with maintaining viability, especially in static culture. The integration of mechanical stimuli was able to extend the lifespan of explants and to induce new bone formation. Bone explant cultures provide unique platforms for bone research and mechanical loading was demonstrated to be an important component in achieving osteogenesis ex vivo. However, more research is needed to establish a representative, reliable, and reproducible bone explant culture system that includes both components of bone remodeling, i.e., formation and resorption, in order to bridge the gap between in vitro and in vivo research in preclinical testing.

Hydrogen Sulfide as Potential Regulatory Gasotransmitter in Arthritic Diseases

The social and economic impact of chronic inflammatory diseases, such as arthritis, explains the growing interest of the research in this field. The antioxidant and anti-inflammatory properties of the endogenous gasotransmitter hydrogen sulfide (H₂S) were recently demonstrated in the context of different inflammatory diseases. In particular, H₂S is able to suppress the production of pro-inflammatory mediations by lymphocytes and innate immunity cells. Considering these biological effects of H₂S, a potential role in the treatment of inflammatory arthritis, such as rheumatoid arthritis (RA), can be postulated. However, despite the growing interest in H₂S, more evidence is needed to understand the pathophysiology and the potential of H₂S as a therapeutic agent. Within this review, we provide an overview on H₂S biological effects, on its role in immune-mediated inflammatory diseases, on H₂S releasing drugs, and on systems of tissue repair and regeneration that are currently under investigation for potential therapeutic applications in arthritic diseases.

A Comparison of Osteoblast and Osteoclast In Vitro Co-Culture Models and Their Translation for Preclinical Drug Testing Applications

As the population of western societies on average ages, the number of people affected by bone remodeling-associated diseases such as osteoporosis continues to increase. The development of new therapeutics is hampered by the high failure rates of drug candidates during clinical testing, which is in part due to the poor predictive character of animal models during preclinical drug testing. Co-culture models of osteoblasts and osteoclasts offer an alternative to animal testing and are considered to have the potential to improve drug development processes in the future. However, a robust, scalable, and reproducible 3D model combining osteoblasts and osteoclasts for preclinical drug testing purposes has not been developed to date. Here we review various types of osteoblast-osteoclast co-culture models and outline the remaining obstacles that must be overcome for their successful translation.

Gaseous signaling molecules and their application in resistant cancer treatment: from invisible to visible

Multidrug resistance (MDR) in cancer remains a critical obstacle for efficient chemotherapy. Many MDR reversal agents have been discovered but failed in clinical trials due to severe toxic effects. Gaseous signaling molecules (GSMs), such as oxygen, nitric oxide, hydrogen sulfide and carbon monoxide, play key roles in regulating cell biological function and MDR. Compared with other toxic chemosensitizing agents, GSMs are endogenous and biocompatible molecules with little side effects. Research show that GSM modulators, including pharmaceutical formulations of GSMs (combined with conventional chemotherapeutic drugs) and GSM-donors (small molecules with GSMs releasing property), can overcome or reverse MDR. This review discusses the roles of these four GSMs in modulating MDR, and summarizes GSMs modulators in treating cancers with drug resistance.

Effects of sulfide and polysulfides transmitted by direct or signal transduction-mediated activation of TRPA1 channels

Hydrogen sulfide (H₂S) is a gaseous mediator in various physiological and pathological processes, including neuroimmune modulation, metabolic pathways, cardiovascular system, tumour growth, inflammation and pain. Now the hydrogen polysulfides (H₂S_n) have been recognised as signalling molecules modulating ion channels, transcription factors and protein kinases. Transient receptor potential (TRP) cation channels can be activated by mechanical, thermal or chemical triggers. Here, we review the current literature regarding the biological actions of sulfide and polysulfide compounds mediated by TRP channels with special emphasis on the role of TRPA1, best known as ion channels in nociceptors. However, the non‐neuronal TRPA1 channels should also be considered to play regulatory roles. Although sulfide and polysulfide effects in different pathological circumstances and TRPA1‐mediated processes have been investigated intensively, our review attempts to present the first comprehensive overview of the potential crosstalk between TRPA1 channels and sulfide‐activated signalling pathways.

Linked Articles

This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc

Dithiolethiones: a privileged pharmacophore for anticancer therapy and chemoprevention

Dithiolethiones are five-membered sulfur-containing cyclic scaffolds that exhibit antioxidative, anti-inflammatory, antithrombic and chemotherapeutic activities. Dithiolethiones display the chemopreventive and cytoprotective effects by activating the antioxidant response element and mounting the transcription of cytoprotective phase II enzymatic machinery. In addition, several classes of dithiolethiones efficiently modulate the activities of proteins that play crucial roles in normal and cancer cells, including glutathione S-transferase, cyclooxygenases and master regulator NF-κB. The present paper summarizes synthetic aspects, pharmacological potentials and biological attributes of dithiolethiones and its derivatives. Additionally, this review concludes with a discussion on how the current state-of-the-art technologies may help in defining a structure–activity relationship of dithiolethiones, thereby facilitating the design and synthesis of potent drug candidates.

International Union of Basic and Clinical Pharmacology. CII: Pharmacological Modulation of H2S Levels: H2S Donors and H2S Biosynthesis Inhibitors

Over the last decade, hydrogen sulfide (H₂S) has emerged as an important endogenous gasotransmitter in mammalian cells and tissues. Similar to the previously characterized gasotransmitters nitric oxide and carbon monoxide, H₂S is produced by various enzymatic reactions and regulates a host of physiologic and pathophysiological processes in various cells and tissues. H₂S levels are decreased in a number of conditions (e.g., diabetes mellitus, ischemia, and aging) and are increased in other states (e.g., inflammation, critical illness, and cancer). Over the last decades, multiple approaches have been identified for the therapeutic exploitation of H₂S, either based on H₂S donation or inhibition of H₂S biosynthesis. H₂S donation can be achieved through the inhalation of H₂S gas and/or the parenteral or enteral administration of so-called fast-releasing H₂S donors (salts of H₂S such as NaHS and Na₂S) or slow-releasing H₂S donors (GYY4137 being the prototypical compound used in hundreds of studies in vitro and in vivo). Recent work also identifies various donors with regulated H₂S release profiles, including oxidant-triggered donors, pH-dependent donors, esterase-activated donors, and organelle-targeted (e.g., mitochondrial) compounds. There are also approaches where existing, clinically approved drugs of various classes (e.g., nonsteroidal anti-inflammatories) are coupled with H₂S-donating groups (the most advanced compound in clinical trials is ATB-346, an H₂S-donating derivative of the non-steroidal anti-inflammatory compound naproxen). For pharmacological inhibition of H₂S synthesis, there are now several small molecule compounds targeting each of the three H₂S-producing enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Although many of these compounds have their limitations (potency, selectivity), these molecules, especially in combination with genetic approaches, can be instrumental for the delineation of the biologic processes involving endogenous H₂S production. Moreover, some of these compounds (e.g., cell-permeable prodrugs of the CBS inhibitor aminooxyacetate, or benserazide, a potentially repurposable CBS inhibitor) may serve as starting points for future clinical translation. The present article overviews the currently known H₂S donors and H₂S biosynthesis inhibitors, delineates their mode of action, and offers examples for their biologic effects and potential therapeutic utility.

Cross-talk of MicroRNA and hydrogen sulfide: A novel therapeutic approach for bone diseases

Bone homeostasis requires a balance between the bone formation of osteoblasts and bone resorption of osteoclasts to maintain ideal bone mass and bone quality. An imbalance in bone remodeling processes results in bone metabolic disorders such as osteoporosis. Hydrogen sulfide (H₂S), a gasotransmitter, has attracted the focus of many researchers due to its multiple physiological functions. It has been implicated in anti-inflammatory, vasodilatory, angiogenic, cytoprotective, anti-oxidative and anti-apoptotic mechanisms. H₂S has also been shown to exert osteoprotective activity through its anti-inflammatory and anti-oxidative effects. However, the underlying molecular mechanisms by which H₂S mitigates bone diseases are not completely understood. Experimental evidence suggests that H₂S may regulate signaling pathways by directly influencing a gene in the cascade or interacting with some other gasotransmitter (carbon monoxide or nitric oxide) or both. MicroRNAs (miRNAs) are short non-coding RNAs which regulate gene expression by targeting, binding and suppressing mRNAs; thus controlling cell fate. Certainly, bone remodeling is also regulated by miRNAs expression and has been reported in many studies. MicroRNAs also regulate H₂S biosynthesis. The inter-regulation of microRNAs and H₂S opens a new possibility for exploring the H₂S-microRNA crosstalk in bone diseases. However, the relationship between miRNAs, bone development, and H₂S is still not well explained. This review focuses on miRNAs and their roles in regulating bone remodeling and possible mechanisms behind H₂S mediated bone loss inhibition, H₂S-miRNAs crosstalk in relation to the pathophysiology of bone remodeling, and future perspectives for miRNA-H₂S as a therapeutic agent for bone diseases.

Methanethiosulfonate derivatives as ligands of the STAT3-SH2 domain

With the aim to discover new STAT3 direct inhibitors, potentially useful as anticancer agents, a set of methanethiosulfonate drug hybrids were synthesized. The in vitro tests showed that all the thiosulfonic compounds were able to strongly and selectively bind STAT3-SH2 domain, whereas the parent drugs were completely devoid of this ability. In addition, some of them showed a moderate antiproliferative activity on HCT-116 cancer cell line. These results suggest that methanethiosulfonate moiety can be considered a useful scaffold in the preparation of new direct STAT3 inhibitors. Interestingly, an unusual kind of organo-sulfur derivative, endowed with valuable antiproliferative activity, was occasionally isolated. [Formula: see text].

Diabetic nephropathy: A potential savior with 'rotten-egg' smell

Diabetic nephropathy (DN) is currently the leading cause of end-stage renal disease. Despite optimal management, DN is still a major contributor to morbidity and mortality of diabetic patients worldwide. The major pathological alterations in DN include excessive accumulation and deposition of extracellular matrix, leading to expansion of mesangial matrix, thickening of glomerular basement membrane and tubulointerstitial fibrosis. At the molecular level, accumulating evidence suggests that hyperglycemia or high glucose mediates renal injury in DN via multiple molecular mechanisms such as induction of oxidative stress, upregulation of renal transforming growth factor beta-1 expression, production of proinflammatory cytokines, activation of fibroblasts and renin angiotensin system, and depletion of adenosine triphosphate. Also worrying is the fact that existing therapies only retard the disease progression but do not prevent it. Therefore, there is urgent need to identify novel therapies to target additional disease mechanisms. Hydrogen sulfide (H₂S), the third member of the gasotransmitter family, has recently been identified and demonstrated to possess important therapeutic characteristics that prevent the development and progression of DN in experimental animals by targeting several important molecular pathways, and therefore may represent an alternative or additional therapeutic approach for DN. This review discusses recent experimental findings on the molecular mechanisms underlying the therapeutic effects of H₂S against the development and progression of DN and its clinical application in the future.

Medical Functions of Hydrogen Sulfide

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

Role of Hydrogen Sulfide in Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) injury is one of the major causes of high morbidity, disability, and mortality in the world. I/R injury remains a complicated and unresolved situation in clinical practice, especially in the field of solid organ transplantation. Hydrogen sulfide (H₂S) is the third gaseous signaling molecule and plays a broad range of physiological and pathophysiological roles in mammals. H₂S could protect against I/R injury in many organs and tissues, such as heart, liver, kidney, brain, intestine, stomach, hind-limb, lung, and retina. The goal of this review is to highlight recent findings regarding the role of H₂S in I/R injury. In this review, we present the production and metabolism of H₂S and further discuss the effect and mechanism of H₂S in I/R injury.

Design, synthesis and evaluation of a series of non-steroidal anti-inflammatory drug conjugates as novel neuroinflammatory inhibitors

Neuroinflammation is involved in the process of several central nervous system (CNS) diseases such as Parkinson's disease, Alzheimer's disease, ischemia and multiple sclerosis. As the macrophages in the central nervous system, microglial cell function in the innate immunity of the brain and are largely responsible for the inflammation-mediated neurotoxicity. Prevention of microglia activation might alleviate neuronal damage and degeneration under the inflammatory conditions, and therefore, represents a possible therapeutic approach to the aforementioned CNS diseases. Here we report the synthesis of a number of non-steroidal anti-inflammatory drug (NSAID) conjugates, and the evaluation of their anti-inflammatory effects in lipopolysaccharide (LPS)-stimulated BV-2 microglial cells and primary mouse microglial cells. Among the tested analogues, compounds 8 and 11 demonstrated potent inhibition of nitric oxide production with no or weak cell toxicity. Compound 8 also significantly suppressed the expression of tumor necrosis factor (TNF)-α, interleukin (IL)-6, cyclooxygenase (COX)-2 as well as inducible nitric oxide synthase (iNOS) in LPS-stimulated BV-2 microglial cells. Further mechanistic studies indicated that compound 8 significantly suppressed phosphorylation of mitogen-activated protein kinases (MAPKs) and subsequent activation of activator of transcription 1 (AP-1). Furthermore, in a co-culture system, compound 8 inhibited the cytotoxicity generated by LPS-activated microglia toward HT-22 neuroblastoma cells. Collectively, these experimental results demonstrated that compound 8 possessed potent anti-neuroinflammatory activity via inhibition of microglia activation, and might serve as a potential lead for the therapeutic treatment of neuroinflammatory diseases.

The therapeutic potential of cystathionine β-synthetase/hydrogen sulfide inhibition in cancer

SIGNIFICANCE

Cancer represents a major socioeconomic problem; there is a significant need for novel therapeutic approaches targeting tumor-specific pathways.

RECENT ADVANCES

In colorectal and ovarian cancers, an increase in the intratumor production of hydrogen sulfide (H2S) from cystathionine β-synthase (CBS) plays an important role in promoting the cellular bioenergetics, proliferation, and migration of cancer cells. It also stimulates peritumor angiogenesis inhibition or genetic silencing of CBS exerts antitumor effects both in vitro and in vivo, and potentiates the antitumor efficacy of anticancer therapeutics.

CRITICAL ISSUES

Recently published studies are reviewed, implicating CBS overexpression and H2S overproduction in tumor cells as a tumor-growth promoting "bioenergetic fuel" and "survival factor," followed by an overview of the experimental evidence demonstrating the anticancer effect of CBS inhibition. Next, the current state of the art of pharmacological CBS inhibitors is reviewed, with special reference to the complex pharmacological actions of aminooxyacetic acid. Finally, new experimental evidence is presented to reconcile a controversy in the literature regarding the effects of H2S donor on cancer cell proliferation and survival.

FUTURE DIRECTIONS

From a basic science standpoint, future directions in the field include the delineation of the molecular mechanism of CBS up-regulation of cancer cells and the delineation of the interactions of H2S with other intracellular pathways of cancer cell metabolism and proliferation. From the translational science standpoint, future directions include the translation of the recently emerging roles of H2S in cancer into human diagnostic and therapeutic approaches.

Sodium hydrosulfide inhibits the differentiation of osteoclast progenitor cells via NRF2-dependent mechanism

Hydrogen sulfide (H2S), which recently emerged as a potent regulator of tissues and organs, is broadly produced in mammalian cells but whether it can regulate bone cell function is still elusive. The main objective of this study was to establish the role of H2S in the regulation of human osteoclast differentiation and function. Sodium hydrosulfide (NaHS), a common H2S-donor, was administered in vitro to CD11b+ human monocytes, the pool of circulating osteoclasts precursors which are critically involved in osteoclast development and function in bone. NaHS dose-dependently decreased human osteoclast differentiation at concentrations which did not induce toxicity. The inhibition of human osteoclast differentiation was associated with a down-regulation in RANKL-dependent intracellular ROS levels in human pre-osteoclasts cells. Furthermore, NaHS up-regulated NRF2 protein expression, its nuclear translocation, and the transcription of the two key downstream antioxidant genes Peroxiredoxin-1 and NAD(P)H dehydrogenase quinone 1, suggesting that NRF2 activation may inhibit human osteoclast differentiation by activating a sustained antioxidant response in osteoclast progenitors; furthermore, NRF2 activators Sulforaphane and Tert-butylhydroquinone inhibited in vitro human osteoclast differentiation. Moreover, silencing NRF2 in human pre-osteoclasts totally abolished NaHS-mediated inhibition of osteoclastogenesis, suggesting that NRF2 is essential to the inhibitory function of NaHS in osteoclast development. Finally, we found that NaHS also downregulated the RANKL/OPG mRNA ratio in human mesenchymal stem cells, the key osteoclast-supporting cells. Our results suggest that NaHS shows a potential therapeutical role in erosive diseases of bone by regulating both direct and indirect mechanisms controlling the differentiation of circulating osteoclasts precursors.

Hydrogen sulfide donors in research and drug development

This review summarized most of the H₂S donors such as inorganic compounds, natural products, anethole trithione derivatives and synthetic compounds used in research and drug development. These special bioactivities provided us some effective strategies for antiphlogosis, cancer therapy, cardiovascular protection and so on.

Hydrogen sulfide prevents H₂O₂-induced senescence in human umbilical vein endothelial cells through SIRT1 activation

The aim of the present study was to investigate the attenuation of endothelial cell senescence by H2S and to explore the mechanisms underlying the anti-aging effects of H2S. Senescence was induced in human umbilical vein endothelial cells (HUVECs) by incubation in 25 µmol/l H2O2 for 1 h. Senescence-associated β-galactosidase (SA-β-gal) activity was examined to determine the effects of H2S on senescent HUVECs. The results indicated that SA-β-gal activity in the H2O2-treated HUVECs was 11.2 ± 1.06%, which was attenuated in the NaHS group. Pretreatment with nicotinamide (NAM), a sirtuin 1 (SIRT1) inhibitor, inhibited the reduction in senescence associated with H2S. Immunoblot analyses revealed that SIRT1 levels in senescent HUVECs treated with NaHS (60 µM) were indistinguishable from controls; however, analyses of SIRT1 activity indicated that SIRT1 enzyme activity was enhanced. In addition, we found that H2S improves the function of senescent HUVECs. The present study demonstrated that H2S protects against HUVEC senescence, potentially through modulation of SIRT1 activity. Furthermore, this study establishes a novel endothelial protective effect of H2S.

The complex effects of the slow-releasing hydrogen sulfide donor GYY4137 in a model of acute joint inflammation and in human cartilage cells

The role of hydrogen sulfide (H₂S) in inflammation remains unclear with both pro- and anti-inflammatory actions of this gas described. We have now assessed the effect of GYY4137 (a slow-releasing H₂S donor) on lipopolysaccharide (LPS)-evoked release of inflammatory mediators from human synoviocytes (HFLS) and articular chondrocytes (HAC) in vitro. We have also examined the effect of GYY4137 in a complete Freund's adjuvant (CFA) model of acute joint inflammation in the mouse. GYY4137 (0.1–0.5 mM) decreased LPS-induced production of nitrite (NO₂⁻), PGE₂, TNF-α and IL-6 from HFLS and HAC, reduced the levels and catalytic activity of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and reduced LPS-induced NF-κB activation in vitro. Using recombinant human enzymes, GYY4137 inhibited the activity of COX-2, iNOS and TNF-α converting enzyme (TACE). In the CFA-treated mouse, GYY4137 (50 mg/kg, i.p.) injected 1 hr prior to CFA increased knee joint swelling while an anti-inflammatory effect, as demonstrated by reduced synovial fluid myeloperoxidase (MPO) and N-acetyl-β-D-glucosaminidase (NAG) activity and decreased TNF-α, IL-1β, IL-6 and IL-8 concentration, was apparent when GYY4137 was injected 6 hrs after CFA. GYY4137 was also anti-inflammatory when given 18 hrs after CFA. Thus, although GYY4137 consistently reduced the generation of pro-inflammatory mediators from human joint cells in vitro, its effect on acute joint inflammation in vivo depended on the timing of administration.