Exogenous hydrogen sulfide donor NaHS alleviates nickel-induced epithelial-mesenchymal transition and the migration of A549 cells by regulating TGF-β1/Smad2/Smad3 signaling

Emerging roles of hydrogen sulfide-metabolizing enzymes in cancer

Gasotransmitters play crucial roles in regulating many physiological processes, including cell signaling, cellular proliferation, angiogenesis, mitochondrial function, antioxidant production, nervous system functions and immune responses. Hydrogen sulfide (H2S) is the most recently identified gasotransmitter, which is characterized by its biphasic behavior. At low concentrations, H2S promotes cellular bioenergetics, whereas at high concentrations, it can exert cytotoxic effects. Cystathionine β-synthetase (CBS), cystathionine-γ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (3-MST), and cysteinyl-tRNA synthetase 2 (CARS2) are pivotal players in H2S biosynthesis in mammalian cells and tissues. The focus of this review is the regulation of the various pathways involved in H2S metabolism in various forms of cancer. Key enzymes in this process include the sulfide oxidation unit (SOU), which includes sulfide:quinone oxidoreductase (SQOR), human ethylmalonic encephalopathy protein 1 (hETHE1), rhodanese, sulfite oxidase (SUOX/SO), and cytochrome c oxidase (CcO) enzymes. Furthermore, the potential role of H2S methylation processes mediated by thiol S-methyltransferase (TMT) and thioether S-methyltransferase (TEMT) is outlined in cancer biology, with potential opportunities for targeting them for clinical translation. In order to understand the role of H2S in oncogenesis and tumor progression, one must appreciate the intricate interplay between H2S-synthesizing and H2S-catabolizing enzymes.

Hydrogen sulfide donor NaHS inhibits formaldehyde-induced epithelial-mesenchymal transition in human lung epithelial cells via activating TGF-β1/Smad2/3 and MAPKs signaling pathways

Formaldehyde (FA) long term exposure leads to abnormal pulmonary function and small airway obstruction of the patients. Hydrogen sulfide (H2S) is one of the recognized gaseous transmitters involved in a wide range of cellular functions. It is unknown the involvement of H2S in FA-induced lung injury. The purpose of this study is to investigate the therapeutic potential and mechanism of H2S on FA-induced epithelial-mesenchymal transition (EMT) of human lung epithelial cells. The cell viability of Beas2B and A549 cells after FA treatment were assessed using MTT assay. The endogenous H2S was visualized by fluorescence microscopy using of the 7-azido-4-methylcoumarin (AzMC). Cell morphology was observed under phase contrast microscope. The mRNAs and proteins level were evaluated by reverse transcription-polymerase chain reaction and western blotting assays. FA treatment downregulated the endogenous H2S levels and the mRNAs and proteins level of H2S synthesizing enzymes, such as cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST) in Beas2B and A549 cells. FA treatment changed the cell morphology of Beas2B cells from cuboid to a spindle-shape, while declined the protein level of E-cadherin and increased the protein level of Vimentin. Moreover, FA treatment increased the proteins level of transforming growth factor-β1 (TGF-β1), phosphorylated-Smad2 (p-Smad2), phosphorylated-Smad3 (p-Smad3), phosphorylated-extracellular signal-regulated kinase (p-ERK), phosphorylated-c-Jun N-terminal kinase (p-JNK), and phosphorylated-P38 (p-P38). Furthermore, the inhibitors of TGF-β receptor type 1 (TGFβRI) and mitogen-activated protein kinases (MAPKs) signaling pathways reversed FA-induced decrease in E-cadherin expression and increase in Vimentin expression in Beas2B cells. Sodium hydrogen sulfide (NaHS) increased the level of H2S, while reversed FA-induced the low expression of E-cadherin and the high expression of Vimentin, TGF-β1, p-Smad2, p-Smad3, p-ERK, p-JNK, and p-P38. These findings indicates FA treatment downregulating the endogenous H2S in human lung epithelial cells. NaHS may inhibit FA-induced EMT in human lung epithelial cells via modulating TGF-β1/Smad2/3 and MAPKs signaling pathways. Therefore, we demonstrated that supplementation of exogenous H2S may inhibit FA-induced lung injury.

Role of hydrogen sulfide in health and disease

In the past, hydrogen sulfide (H2S) was recognized as a toxic and dangerous gas; in recent years, with increased research, we have discovered that H2S can act as an endogenous regulatory transmitter. In mammals, H2S-catalyzing enzymes, such as cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase, are differentially expressed in a variety of tissues and affect a variety of biological functions, such as transcriptional and posttranslational modification of genes, activation of signaling pathways in the cell, and metabolic processes in tissues, by producing H2S. Various preclinical studies have shown that H2S affects physiological and pathological processes in the body. However, a detailed systematic summary of these roles in health and disease is lacking. Therefore, this review provides a thorough overview of the physiological roles of H2S in different systems and the diseases associated with disorders of H2S metabolism, such as ischemia-reperfusion injury, hypertension, neurodegenerative diseases, inflammatory bowel disease, and cancer. Meanwhile, this paper also introduces H2S donors and novel release modes, as well as the latest preclinical experimental results, aiming to provide researchers with new ideas to discover new diagnostic targets and therapeutic options.

Dextran-Based Antibacterial Hydrogel Dressings for Accelerating Infected Wound Healing by Reducing Inflammation Levels

Infected wounds pose challenges such as exudate management, bacterial infections, and persistent inflammation, making them a significant challenge for modern dressings. To address these issues in infected wounds more effectively, aerogel-hydrogel biphase gels based on dextran are developed. The gel introduced in this study exhibits antibacterial and anti-inflammatory properties in the process of wound therapy, contributing to accelerated wound healing. The aerogel phase exhibits exceptional water-absorption capabilities, rapidly soaking up exudate from infected wound, thereby fostering a clean and hygienic wound healing microenvironment. Concurrently, the aerogel phase is enriched with hydrogen sulfide donors. Following water absorption and the formation of the hydrogel phase, it enables the sustained release of hydrogen sulfide around the wound sites. The experiments confirm that hydrogen sulfide, by promoting M2 macrophage differentiation and reducing the levels of inflammatory factors, effectively diminishes local inflammation levels at the wound site. Furthermore, the sodium copper chlorophyllin component within the hydrogel phase demonstrates effective antibacterial properties through photodynamic antimicrobial therapy, providing a viable solution to wound infection challenges.

Recent advances in the role of hydrogen sulfide in age-related diseases

In recent years, the impact of age-related diseases on human health has become increasingly severe, and developing effective drugs to deal with these diseases has become an urgent task. Considering the essential regulatory role of hydrogen sulfide (H2S) in these diseases, it is regarded as a promising target for treatment. H2S is a novel gaseous transmitter involved in many critical physiological activities, including anti-oxidation, anti-inflammation, and angiogenesis. H2S also regulates cell activities such as cell proliferation, migration, invasion, apoptosis, and autophagy. These regulatory effects of H2S contribute to relieving and treating age-related diseases. In this review, we mainly focus on the pathogenesis and treatment prospects of H2S in regulating age-related diseases.

Value of exhaled hydrogen sulfide in early diagnosis of esophagogastric junction adenocarcinoma

Esophagogastric junction adenocarcinoma (EJA) has increased in recent years, and it exhibits a poor prognosis and a short survival period for patients. Hydrogen sulfide (H2S) plays an important role in the pathogenesis of cancer and has been studied as a diagnostic factor in some tumor diseases. However, few studies have explored the diagnostic value of H2S for EJA. In the present study, a total of 56 patients with early-stage EJA were enrolled while 57 healthy individuals were selected as the healthy control group. Clinical features were recorded, and exhaled H2S and blood samples were collected from both groups. Exhaled H2S and serum interleukin-8 (IL-8) expression levels were detected in both groups. The correlation between exhaled H2S and serum IL-8 levels was analyzed using Pearson's correlation method. Receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of exhaled H2S combined with IL-8 detection in EJA. The results showed that patients with EJA exhaled more H2S than healthy individuals. In addition, exhaled H2S was positively correlated with increased IL-8 expression. The ROC curve revealed that the exhaled H2S test had an acceptable diagnostic effect and could be used to diagnose EJA. The increase in H2S exhaled by patients with EJA indicated that H2S may be related to the occurrence and development of EJA; however, the in vivo mechanism needs to be further explored. Collectively, it was determined in the present study that exhaled H2S was significantly higher in patients with early-stage EJA than in healthy controls and combined diagnosis with patient serum IL-8 could improve diagnostic accuracy, which has potential diagnostic value for early diagnosis and screening of EJA.

Nickel chloride promotes lung cancer invasion and metastasis by up-regulating the expression of E3 ubiquitin ligase TRIM31 through the IL-6/STAT3 signaling axis

Nickel compounds are widely used in industries and daily life as important industrial products. Long-term exposure to nickel compounds has been associated with increased incidence and poor prognosis of lung cancer. However, the molecular mechanism by which exposure to nickel compounds induces the malignant phenotype of lung cancer cells remains unclear. In this study, we confirmed that nickel chloride (NiCl2) exposure promotes invasion and metastasis through IL-6/STAT3 both in vitro and vivo. Mechanistically, we found that NiCl2 mediated the transcriptional regulation of E3 ubiquitin ligase TRIM31 by SATAT3 phosphorylation, and promoted its up-regulation. Overexpression TRIM31 is an independent risk factor for lung cancer patients, and it promotes the invasion and metastasis of lung cancer cells. In addition, E3 ubiquitination ligase TRIM31 binds to its substrate TP53 protein in the RING region and accelerates TP53 protein ubiquitination and degradation. Functional recovery experiments showed that NiCl2 exposure promotes the invasion and metastasis ability of lung cancer and ubiquitination-mediated degradation of TP53 protein through the STAT3/TRIM31 axis. These findings reveal the role and mechanism of NiCl2 in lung cancer progression, indicating that STAT3 and TRIM31 may be promising targets for the treatment of lung cancer.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Sodium thiosulfate inhibits epithelial-mesenchymal transition in melanoma via regulating the Wnt/β-catenin signaling pathway

BACKGROUND

Melanoma is the most common form of skin cancer. Given its high metastasis and high recurrence, its therapies are constantly updated.

OBJECTIVE

The study aims to prove the efficacy of sodium thiosulfate (STS), an antidote to cyanide or nitroprusside poisoning, in melanoma treatment.

METHODS

We tested the effect of STS by culturing melanoma cells (B16 and A375) in vitro and establishing melanoma mouse models in vivo. The proliferation and viability of melanoma cells were measured by the CCK-8 test, cell cycle assay, apoptosis analysis, wound healing assay, and transwell migration assay. The expression of apoptosis-related molecules, epithelial-mesenchymal transition (EMT)-associated molecules, and the Wnt/β-catenin signaling pathway-related molecules were determined by Western blotting and immunofluorescence.

RESULTS

The high metastasis of melanoma is considered to be linked to the EMT process. The scratch assay using B16 and A375 cells also showed that STS could inhibit the EMT process of melanoma. We demonstrated that STS inhibited the proliferation, viability, and EMT process of melanoma by releasing H₂S. STS-mediated weakening of cell migration was related to the inhibition of the Wnt/β-catenin signaling pathway. Mechanistically, we defined that STS inhibited the EMT process via the Wnt/β-catenin signaling pathway.

CONCLUSIONS

These results suggest that the negative effect of STS on melanoma development is mediated by the reduction of EMT via the regulation of the Wnt/β-catenin signaling pathway, which provides a new clue to treating melanoma.

Endoplasmic reticulum stress mediates nickel chloride-induced epithelial‑mesenchymal transition and migration of human lung cancer A549 cells through Smad2/3 and p38 MAPK activation

BACKGROUND

The endoplasmic reticulum (ER) is a cellular membrane-bound organelle whereby proteins are synthesized, folded and glycosylated. Due to intrinsic (e.g., genetic) and extrinsic (e.g., environmental stressors) perturbations, ER proteostasis can be deregulated within cells which triggers unfolded protein response (UPR) as an adaptive stress response that may impact the migration and invasion properties of cancer cells. However, the mechanisms underlying the nickel compounds on lung cancer cell migration and invasion remain uncertain.

OBJECTIVE

We aimed to study whether Nickel chloride (NiCl₂) induces ER stress in lung cancer cells, and whether ER stress is involved in modulating epithelial-mesenchymal transition (EMT) and migration by Smads and MAPKs pathways activation following NiCl₂ treatment.

METHODS

A549 cells were treated with NiCl₂ to determine the cell viability using MTT assay. The wound healing assay was used to evaluate cell migration ability. ER ultrastructure was observed by transmission electron microscopy. Western blotting assay was performed to evaluate the protein levels of BIP, PERK, IRE-1α, XBP-1 s, and ATF6 for ER stress and UPR, E-cadherin and Vimentin for EMT, p-Smad2/3, p-ERK, p-JNK, and p-P38 for activation of Smads and MAPKs signaling pathways.

RESULTS

The expression levels of BIP, PERK, IRE-1α, XBP-1 s, and ATF6 were significantly increased following treatment with NiCl₂ in time- and dose-effect relationship. The ER stress inhibitor 4-PBA downregulated the expression levels of the above five proteins, and reversed the decrease in E-cadherin protein level and the increase in vimentin protein expression and cell migration abilities caused by NiCl₂. Furthermore, 4-PBA significantly reduced nickel chloride-induced Smad2/3 and p38 MAPK pathway activation, while not affected ERK and JNK MAPK pathways.

CONCLUSION

NiCl₂ triggers ER stress and UPR in A549 cells. Moreover, 4-PBA alleviates NiCl₂-induced EMT and migration ability of A549 cells possibly through the Smad2/3 and p38 MAPK pathways activation, rather than ERK and JNK MAPK pathways.

The Role of Hydrogen Sulfide in the Development and Progression of Lung Cancer

Lung cancer is one of the 10 most common cancers in the world, which seriously affects the normal life and health of patients. According to the investigation report, the 3-year survival rate of patients with lung cancer is less than 20%. Heredity, the environment, and long-term smoking or secondhand smoke greatly promote the development and progress of the disease. The mechanisms of action of the occurrence and development of lung cancer have not been fully clarified. As a new type of gas signal molecule, hydrogen sulfide (H₂S) has received great attention for its physiological and pathological roles in mammalian cells. It has been found that H₂S is widely involved in the regulation of the respiratory system and digestive system, and plays an important role in the occurrence and development of lung cancer. H₂S has the characteristics of dissolving in water and passing through the cell membrane, and is widely expressed in body tissues, which determines the possibility of its participation in the occurrence of lung cancer. Both endogenous and exogenous H₂S may be involved in the inhibition of lung cancer cells by regulating mitochondrial energy metabolism, mitochondrial DNA integrity, and phosphoinositide 3-kinase/protein kinase B co-pathway hypoxia-inducible factor-1α (HIF-1α). This article reviews and discusses the molecular mechanism of H₂S in the development of lung cancer, and provides novel insights for the prevention and targeted therapy of lung cancer.

Hydrogen Sulfide Biology and Its Role in Cancer

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

Hydrogen sulfide and metal interaction: the pathophysiological implications

Hydrogen sulfide (H₂S), previously recognized as a toxic gas, has emerged as an important gaseous signaling molecule along with nitric oxide, carbon monoxide and also hydrogen. H₂S can be endogenously produced in the mammalian body at a very low level for various pathophysiological processes. Notably, H₂S can interact with several essential metals in the body such as iron, copper, nickel, and zinc to carry out specific functions. The interactions of H₂S with metal-binding proteins have been shown to aid in its signal transduction and cellular metabolism. In addition, H₂S is capable of providing a cytoprotective role against metal toxicity. As the research in the field of H₂S signaling in biology and medicine increases, much progresses have been developed for detecting H₂S via interaction with metals. In this review, the interaction of H₂S with metals, specifically in regard to metal-driven metabolism of H₂S, the protection against metal toxicity by H₂S and the detection of H₂S using metals will be discussed. Discovering the interactions of this gasotransmitter with metals is important for determining the mechanisms underlying the cellular functions of H₂S as well as developing novel therapeutic avenues.

Application of a fluorescent H2S probe based on excited-state intramolecular proton transfer for detecting latent mechanism of H2S-induced MCF-7 apoptosis

Background: H₂S is the third gas transmitter affecting the growth, reproduction and survival of cancer cells. However, the H₂S anticancer and antitumor mechanism still needs to be further studied. Methods: Here, FHS-1 was synthesized utilizing excited-state intramolecular proton transfer to detect H₂S in MCF-7 cells, and investigated the effects of varying concentrations NaHS on apoptosis. Results: The study found that FHS-1 detects H₂S levels with high selectivity and pH stability and that H₂S may regulate apoptosis in MCF-7 cells through the p53/mTOR/STAT3 pathway. Conclusion: Researching the influence of H₂S on apoptosis can serve as a theoretical foundation for future research into H₂S-related anticancer medicines, and the H₂S probe can be used as an effective cancer screening tool.

Transcriptional repression of E-cadherin in nickel-exposed lung epithelial cells mediated by loss of Sp1 binding at the promoter

E-cadherin plays a central role in the stability of epithelial tissues by facilitating cell-cell adhesion. Loss of E-cadherin expression is a hallmark of epithelial-mesenchymal transition (EMT), a major event in the pathogenesis of several lung diseases. Our earlier studies showed that nickel, a ubiquitous environmental toxicant, induced EMT by persistently downregulating E-cadherin expression in human lung epithelial cells and that the EMT remained irreversible postexposure. However, the molecular basis of persistent E-cadherin downregulation by nickel exposure is not understood. Here, our studies show that the binding of transcription factor Sp1 to the promoter of E-cadherin encoding gene, CDH1, is essential for its expression. Nickel exposure caused a loss of Sp1 binding at the CDH1 promoter, resulting in its downregulation and EMT induction. Loss of Sp1 binding at the CDH1 promoter was associated with an increase in the binding of ZEB1 adjacent to the Sp1 binding site. ZEB1, an EMT master regulator persistently upregulated by nickel exposure, is a negative regulator of CDH1. CRISPR-Cas9-mediated knockout of ZEB1 restored Sp1 binding at the CDH1 promoter. Furthermore, ZEB1 knockout rescued E-cadherin expression and re-established the epithelial phenotype. Since EMT is associated with a number of nickel-exposure-associated chronic inflammatory lung diseases including asthma, fibrosis and cancer and metastasis, our findings provide new insights into the mechanisms associated with nickel pathogenesis.

Nickel chloride induces spermatogenesis disorder by testicular damage and hypothalamic-pituitary-testis axis disruption in mice

As a common environmental pollutant, nickel chloride (NiCl₂) poses serious threat to human and animals health. NiCl₂ has adverse effects on reproductive function in male, however, the underlying mechanisms are not fully illuminated. In this study, 64 male ICR mice were divided into four groups (8 mice per each period/ group), in which mice orally administrated with 0, 7.5, 15 or 30 mg/kg body weight for 14 or 28 consecutive days, respectively. The results showed that the sperm concentration (12.95%, 29.78% and 37.63% -) and sperm motility (19.79%, 34.88% and 43.10%) were dose-dependent significantly reduced, and the total sperm malformation rates (110.15%, 206.84% and 292.27%) were dose-dependent significantly elevated in the 7.5, 15 and 30 mg/kg NiCl₂ treatment groups (vs control at 28 days), respectively (P < 0.05). Meanwhile, NiCl₂ also decreased the relative weights of testis and epididymis and caused histopathological lesions of testis and epididymis. Furthermore, serum testosterone levels were significantly decreased after NiCl₂ treatment. And the findings showed that NiCl₂ down-regulated the expression of LH-R, StAR, P450scc, 3β-HSD, 17β-HSD, ABP and INHβB in the testis, however, the relative genes in the hypothalamus (Kiss-1, GPR54 and GnRH) and pituitary (GnRH-R, LHβ and FSHβ) did not exhibit noticeable change. In summary, NiCl₂ induced spermatogenesis disorder by testicular damage and hypothalamic-pituitary-testis axis disruption in mice, and only impaired the genes on the testis of HPT axis.

Epithelial-mesenchymal transition: Insights into nickel-induced lung diseases

Nickel compounds are environmental toxicants, prevalent in the atmosphere due to their widespread use in several industrial processes, extensive consumption of nickel containing products, as well as burning of fossil fuels. Exposure to nickel is associated with a multitude of chronic inflammatory lung diseases including asthma, chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. In addition, nickel exposure is implicated in the development of nasal and lung cancers. Interestingly, a common pathogenic mechanism underlying the development of diseases associated with nickel exposure is epithelial-mesenchymal transition (EMT). EMT is a process by which the epithelial cells lose their junctions and polarity and acquire mesenchymal traits, including increased ability to migrate and invade. EMT is a normal and essential physiological process involved in differentiation, development and wound healing. However, EMT also contributes to a number of pathological conditions, including fibrosis, cancer and metastasis. Growing evidence suggest that EMT induction could be an important outcome of nickel exposure. In this review, we discuss the role of EMT in nickel-induced lung diseases and the mechanisms associated with EMT induction by nickel exposure.

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

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

The Hidden Role of Hydrogen Sulfide Metabolism in Cancer

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

Pharmacological induction of mesenchymal-epithelial transition via inhibition of H2S biosynthesis and consequent suppression of ACLY activity in colon cancer cells

Hydrogen sulfide (H₂S) is an important endogenous gaseous transmitter mediator, which regulates a variety of cellular functions in autocrine and paracrine manner. The enzymes responsible for the biological generation of H₂S include cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). Increased expression of these enzymes and overproduction of H₂S has been implicated in essential processes of various cancer cells, including the stimulation of metabolism, maintenance of cell proliferation and cytoprotection. Cancer cell identity is characterized by so-called "transition states". The progression from normal (epithelial) to transformed (mesenchymal) state is termed epithelial-to-mesenchymal transition (EMT) whereby epithelial cells lose their cell-to-cell adhesion capacity and gain mesenchymal characteristics. The transition process can also proceed in the opposite direction, and this process is termed mesenchymal-to-epithelial transition (MET). The current project was designed to determine whether inhibition of endogenous H₂S production in colon cancer cells affects the EMT/MET balance in vitro. Inhibition of H₂S biosynthesis in HCT116 human colon cancer cells was achieved either with aminooxyacetic acid (AOAA) or 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE). These inhibitors induced an upregulation of E-cadherin and Zonula occludens-1 (ZO-1) expression and downregulation of fibronectin expression, demonstrating that H₂S biosynthesis inhibitors can produce a pharmacological induction of MET in colon cancer cells. These actions were functionally reflected in an inhibition of cell migration, as demonstrated in an in vitro "scratch wound" assay. The mechanisms involved in the action of endogenously produced H₂S in cancer cells in promoting (or maintaining) EMT (or tonically inhibiting MET) relate, at least in part, in the induction of ATP citrate lyase (ACLY) protein expression, which occurs via upregulation of ACLY mRNA (via activation of the ACLY promoter). ACLY in turn, regulates the Wnt-β-catenin pathway, an essential regulator of the EMT/MET balance. Taken together, pharmacological inhibition of endogenous H₂S biosynthesis in cancer cells induces MET. We hypothesize that this may contribute to anti-cancer / anti-metastatic effects of H₂S biosynthesis inhibitors.

Keap1-Nrf2 pathway up-regulation via hydrogen sulfide mitigates polystyrene microplastics induced-hepatotoxic effects

Microplastics, which are new types of environmental pollutants, are recently receiving widespread attention worldwide. Hydrogen sulfide (H₂S) as the third endogenous gaseous mediator had protective effects in multiple physiological and pathological conditions. However, the protective role of H₂S in microplastics-induced hepatotoxocity remain unclear. In this study, our data showed that H₂S significantly suppressed inflammation, apoptosis and oxidative stress induced by polystyrene microplastics (mic-PS) (20 mg/kg b.w.) in the liver. Strikingly, although mic-PS exposure increased the expression of nuclear factor-E2-related factor (Nrf2), it did not influence the levels of heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQOl) in the L02 hepatocytes. Immunofluorescence assay showed that sodium hydrosulfide (NaHS) reduced micro-Ps-induced hepatic apoptosis by facilitating nuclear accumulation of Nrf2. Simultaneously, flow cytometry also showed that NaHS could prevent mic-PS-induced accumulation of reactive oxygen species (ROS) by increasing the expression of HO-1 and NQO1. Furthermore, inhibition of HO-1 could reverse the hepatic protective effects of NaHS during mic-PS exposure. Mechanistically, H₂S elevating the HO-1 and NQO1 expression by facilitating nuclear accumulation of Nrf2, and consequently reducing mic-PS-induced hepatic apoptosis and inflammation. This study unveils the hepatotoxic effects of MPs and suggest NaHS have protective effects on mic-PS-induced liver damage.

Role of hydrogen sulfide donors in cancer development and progression

In recent years, a vast number of potential cancer therapeutic targets have emerged. However, developing efficient and effective drugs for the targets is of major concern. Hydrogen sulfide (H2S), one of the three known gasotransmitters, is involved in the regulation of various cellular activities such as autophagy, apoptosis, migration, and proliferation. Low production of H2S has been identified in numerous cancer types. Treating cancer cells with H2S donors is the common experimental technique used to improve H2S levels; however, the outcome depends on the concentration/dose, time, cell type, and sometimes the drug used. Both natural and synthesized donors are available for this purpose, although their effects vary independently ranging from strong cancer suppressors to promoters. Nonetheless, numerous signaling pathways have been reported to be altered following the treatments with H2S donors which suggest their potential in cancer treatment. This review will analyze the potential of H2S donors in cancer therapy by summarizing key cellular processes and mechanisms involved.