Hydrogen Sulfide Oxidation: Adaptive Changes in Mitochondria of SW480 Colorectal Cancer Cells upon Exposure to Hypoxia

Endoplasmic reticulum protein of 57 kDa sulfhydration promotes intestinal calcium absorption to attenuate primary osteoporosis

Endogenous hydrogen sulfide (H2S) plays an important role in bone metabolism. However, the exact role of H2S in intestinal calcium and phosphorus absorption and its potential in preventing and treating primary osteoporosis remains unknown. Therefore, this study aimed to investigate the potential of H2S in promoting intestinal calcium and phosphorus absorption and alleviating primary osteoporosis. We measured the apparent absorptivity of calcium, femoral bone density, expression and sulfhydration of the duodenal endoplasmic reticulum protein of 57 kDa (ERp57), duodenal cystathionine γ-lyase (CSE) expression, and serum H2S content in adult and old CSE-knockout and wild-type mice. We also assessed intracellular reactive oxygen species (ROS) and Ca2+ content in CSE-overexpressing or knockout intestinal epithelial cell (IEC)-6 cells. In senile mice, CSE knockout decreased endogenous H2S, ERp57 sulfhydration, and intestinal calcium absorption and worsened osteoporosis, which were partially reversed by GYY4137, an H2S donor. CSE overexpression in IEC-6 cells increased ERp57 sulfhydration, protein kinase A and C activity, and intracellular Ca2+, whereas CSE knockout exerted the opposite effects. Furthermore, hydrogen peroxide (H2O2) stimulation had similar effects as in CSE knockout, which were reversed by pretreatment with sodium hydrosulfide before H2O2 stimulation and restored by DL-dithiothreitol. These findings suggest that H2S attenuates primary osteoporosis by preventing ROS-induced ERp57 damage in intestinal epithelial cells by enhancing ERp57 activity and promoting intestinal calcium absorption, thereby aiding in developing therapeutic interventions to prevent osteoporosis.

A curcumin-loaded biopolymeric nanocomposite alleviates dextran sulfate sodium induced ulcerative colitis via suppression of inflammation and oxidative stress

Functional drugs nano delivery systems manufactured from natural active products are promising for the field of biomedicines. In this study, an anti-ulcerative colitis (UC) curcumin loaded biopolymeric nanocomposite (CZNH) was fabricated and investigated. CZNH nanocomposite was obtained using the anti-solvent precipitation method, wherein curcumin-loaded zein colloidal particles served as the core, while sodium casein (NaCas) and hyaluronic acid (HA) formed the outermost layer of CZNH nanocomposite. Fourier transform infrared (FT-IR) spectrum and transmission electron microscopy (TEM) findings demonstrated that CZNH nanocomposite was a double-layer spherical micelle (250 nm) resulting from the hydrogen bond interactions and electrostatic adsorptions between zein, NaCas, and HA. Furthermore, CZNH nanocomposite exhibited prominent resuspension and storage stability in aqueous solution, which can be stored at 4 °C for approximately 30 days. In vivo anti-UC studies showed that CZNH nanocomposite could effectively alleviate UC symptoms via mediating inflammatory factors [tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6], myeloperoxidase (MPO), and oxidative stress factor [malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px)]. This study suggested that the CZNH nanocomposite showed great promise as an efficient curcumin nanocarrier for UC therapy.

Hydrogen sulfide (H2S) metabolism: Unraveling cellular regulation, disease implications, and therapeutic prospects for precision medicine

Hydrogen sulfide (H2S), traditionally recognized as a noxious gas with a pungent odor, has emerged as a fascinating metabolite originating from proteinaceous foods. This review provides a comprehensive examination of H2S regulatory metabolism in cell. Dysregulation of cellular processes plays a pivotal role in the pathogenesis of numerous diseases. Recent development explores the chemistry of biosynthesis and degradation of H2S in cells. The consequences of dysregulation causing diseases and the emerging role of hydrogen sulfide (H2S) modulation as a promising therapeutic platform has not been explored much. These disturbances can manifest as oxidative stress, inflammation, and aberrant cellular signaling pathways, contributing to the development and progression of diseases such as cancer, cardiovascular disorders, neurodegenerative diseases, and diabetes. Hydrogen sulfide has gained recognition as a key player in cellular regulation. H2S is involved in numerous physiological processes, including vasodilation, inflammation control, and cytoprotection. Recent advances in research have focused on modulating H2S levels to restore cellular balance and mitigate disease progression. This approach involves both exogenous H2S donors and inhibitors of H2S -producing enzymes. By harnessing the versatile properties of H2S, researchers and clinicians may develop innovative therapies that address the root causes of dysregulation-induced diseases. As our understanding of H2S biology deepens, the potential for precision medicine approaches tailored to specific diseases becomes increasingly exciting, holding the promise of improved patient outcomes and a new era in therapeutics.

Sulfide:quinone oxidoreductase alleviates ferroptosis in acute kidney injury via ameliorating mitochondrial dysfunction of renal tubular epithelial cells

Ferroptosis is iron-dependent and regulates necrosis caused by lipid peroxidation and mitochondrial damage. Recent evidence has revealed an emerging role for ferroptosis in the pathophysiology of acute kidney injury (AKI). Sulfide:quinone oxidoreductase (SQOR) is a mitochondrial inner membrane protein highly expressed in the renal cortex. However, the effects of SQOR on ferroptosis and AKI have not been elucidated. In this study, we evaluated the effects of SQOR in several AKI models. We observed a rapid decrease in SQOR expression after cisplatin stimulation in both in vivo and in vitro models. SQOR-deletion mice exhibit exacerbated kidney impairment and ferroptosis in renal tubular epithelial cells following cisplatin injury. Additionally, our results showed that the overexpression of SQOR or ADT-OH (the slow-releasing H2S donor) preserved renal function in the three AKI mouse models. These effects were evidenced by lower levels of serum creatinine (SCr), blood urea nitrogen (BUN), renal neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury molecule 1 (KIM-1). Importantly, SQOR knockout significantly aggravates cisplatin-induced ferroptosis by promoting mitochondrial dysfunction in renal tubular epithelial cells (RTECs). Moreover, online database analysis combined with our study revealed that SYVN1, an upregulated E3 ubiquitin ligase, may mediate the ubiquitin-mediated degradation of SQOR in AKI. Consequently, our results suggest that SYVN1-mediated ubiquitination degradation of SQOR may induce mitochondrial dysfunction in RTECs, exacerbating ferroptosis and thereby promoting the occurrence and development of AKI. Hence, targeting the SYVN1-SQOR axis could be a potential therapeutic strategy for AKI treatment.

Hydrogen Sulfide: Physiological Roles and Therapeutic Implications against COVID-19

The COVID-19 pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) poses a major menace to economic and public health worldwide. Angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2) are two host proteins that play an essential function in the entry of SARS-- COV-2 into host cells. Hydrogen sulfide (H2S), a new gasotransmitter, has been shown to protect the lungs from potential damage through its anti-inflammatory, antioxidant, antiviral, and anti-aging effects. It is well known that H2S is crucial in controlling the inflammatory reaction and the pro-inflammatory cytokine storm. Therefore, it has been suggested that some H2S donors may help treat acute lung inflammation. Furthermore, recent research illuminates a number of mechanisms of action that may explain the antiviral properties of H2S. Some early clinical findings indicate a negative correlation between endogenous H2S concentrations and COVID-19 intensity. Therefore, reusing H2S-releasing drugs could represent a curative option for COVID-19 therapy.

Thiol reductive stress activates the hypoxia response pathway

Owing to their capability to disrupt the oxidative protein folding environment in the endoplasmic reticulum (ER), thiol antioxidants, such as dithiothreitol (DTT), are used as ER-specific stressors. We recently showed that thiol antioxidants modulate the methionine-homocysteine cycle by upregulating an S-adenosylmethionine-dependent methyltransferase, rips-1, in Caenorhabditis elegans. However, the changes in cellular physiology induced by thiol stress that modulate the methionine-homocysteine cycle remain uncharacterized. Here, using forward genetic screens in C. elegans, we discover that thiol stress enhances rips-1 expression via the hypoxia response pathway. We demonstrate that thiol stress activates the hypoxia response pathway. The activation of the hypoxia response pathway by thiol stress is conserved in human cells. The hypoxia response pathway enhances thiol toxicity via rips-1 expression and confers protection against thiol toxicity via rips-1-independent mechanisms. Finally, we show that DTT might activate the hypoxia response pathway by producing hydrogen sulfide. Our studies reveal an intriguing interaction between thiol-mediated reductive stress and the hypoxia response pathway and challenge the current model that thiol antioxidant DTT disrupts only the ER milieu in the cell.

Recent advances in the role of endogenous hydrogen sulphide in cancer cells

Hydrogen sulphide (H2 S) is a gaseous neurotransmitter that can be self-synthesized by living organisms. With the deepening of research, the pathophysiological mechanisms of endogenous H2 S in cancer have been increasingly elucidated: (1) promote angiogenesis, (2) stimulate cell bioenergetics, (3) promote migration and proliferation thereby invasion, (4) inhibit apoptosis and (5) activate abnormal cell cycle. However, the increasing H2 S levels via exogenous sources show the opposite trend. This phenomenon can be explained by the bell-shaped pharmacological model of H2 S, that is, the production of endogenous (low concentration) H2 S promotes tumour growth while the exogenous (high concentration) H2 S inhibits tumour growth. Here, we review the impact of endogenous H2 S synthesis and metabolism on tumour progression, summarize the mechanism of action of H2 S in tumour growth, and discuss the possibility of H2 S as a potential target for tumour treatment.

A Water-Soluble Hydrogen Sulfide Donor Suppresses the Growth of Hepatocellular Carcinoma via Inhibiting the AKT/GSK-3β/β-Catenin and TGF-β/Smad2/3 Signaling Pathways

Hepatocellular carcinoma (HCC) is a disease with high morbidity, high mortality, and low cure rate. Hyaluronic acid (HA) is widely adopted in tissue engineering and drug delivery. 5-(4-Hydroxyphenyl)-3H-1, 2-dithiol-3-thione (ADT-OH) is one of commonly used H₂S donors. In our previous study, HA-ADT was designed and synthesized via coupling of HA and ADT-OH. In this study, compared with sodium hydrosulfide (NaHS, a fast H₂S-releasing donor) and morpholin-4-ium (4-methoxyphenyl)-morpholin-4-ylsulfanylidenesulfido-λ5-phosphane (GYY4137, a slow H₂S-releasing donor), HA-ADT showed stronger inhibitory effect on the proliferation, migration, invasion, and cell cycle of human HCC cells. HA-ADT promoted apoptosis by suppressing the expressions of phospho (p)-protein kinase B (PKB/AKT), p-glycogen synthase kinase-3β (GSK-3β), p-β-catenin, and also inhibited autophagy via the downregulation of the protein levels of p-Smad2, p-Smad3, and transforming growth factor-β (TGF-β) in human HCC cells. Moreover, HA-ADT inhibited HCC xenograft tumor growth more effectively than both NaHS and GYY4137. Therefore, HA-ADT can suppress the growth of HCC cells by blocking the AKT/GSK-3β/β-catenin and TGF-β/Smad2/3 signaling pathways. HA-ADT and its derivatives may be developed as promising antitumor drugs.

Hydrogen Sulfide and Its Donors: Keys to Unlock the Chains of Nonalcoholic Fatty Liver Disease

Hydrogen sulfide (H2S) has emerged as the third “gasotransmitters” and has a crucial function in the diversity of physiological functions in mammals. In particular, H2S is considered indispensable in preventing the development of liver inflammation in the case of excessive caloric ingestion. Note that the concentration of endogenous H2S was usually low, making it difficult to discern the precise biological functions. Therefore, exogenous delivery of H2S is conducive to probe the physiological and pathological roles of this gas in cellular and animal studies. In this review, the production and metabolic pathways of H2S in vivo, the types of donors currently used for H2S release, and study evidence of H2S improvement effects on nonalcoholic fatty liver disease are systematically introduced.

Sequential Accumulation of ‘Driver’ Pathway Mutations Induces the Upregulation of Hydrogen-Sulfide-Producing Enzymes in Human Colonic Epithelial Cell Organoids

Recently, a CRISPR-Cas9 genome-editing system was developed with introduced sequential ‘driver’ mutations in the WNT, MAPK, TGF-β, TP53 and PI3K pathways into organoids derived from normal human intestinal epithelial cells. Prior studies have demonstrated that isogenic organoids harboring mutations in the tumor suppressor genes APC, SMAD4 and TP53, as well as the oncogene KRAS, assumed more proliferative and invasive properties in vitro and in vivo. A separate body of studies implicates the role of various hydrogen sulfide (H2S)-producing enzymes in the pathogenesis of colon cancer. The current study was designed to determine if the sequential mutations in the above pathway affect the expression of various H2S producing enzymes. Western blotting was used to detect the expression of the H2S-producing enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST), as well as several key enzymes involved in H2S degradation such as thiosulfate sulfurtransferase/rhodanese (TST), ethylmalonic encephalopathy 1 protein/persulfide dioxygenase (ETHE1) and sulfide-quinone oxidoreductase (SQR). H2S levels were detected by live-cell imaging using a fluorescent H2S probe. Bioenergetic parameters were assessed by Extracellular Flux Analysis; markers of epithelial-mesenchymal transition (EMT) were assessed by Western blotting. The results show that the consecutive mutations produced gradual upregulations in CBS expression—in particular in its truncated (45 kDa) form—as well as in CSE and 3-MST expression. In more advanced organoids, when the upregulation of H2S-producing enzymes coincided with the downregulation of the H2S-degrading enzyme SQR, increased H2S generation was also detected. This effect coincided with the upregulation of cellular bioenergetics (mitochondrial respiration and/or glycolysis) and an upregulation of the Wnt/β-catenin pathway, a key effector of EMT. Thus sequential mutations in colon epithelial cells according to the Vogelstein sequence are associated with a gradual upregulation of multiple H2S generating pathways, which, in turn, translates into functional changes in cellular bioenergetics and dedifferentiation, producing more aggressive and more invasive colon cancer phenotypes.

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.

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

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.

Cysteine as a Multifaceted Player in Kidney, the Cysteine-Related Thiolome and Its Implications for Precision Medicine

In this review encouraged by original data, we first provided in vivo evidence that the kidney, comparative to the liver or brain, is an organ particularly rich in cysteine. In the kidney, the total availability of cysteine was higher in cortex tissue than in the medulla and distributed in free reduced, free oxidized and protein-bound fractions (in descending order). Next, we provided a comprehensive integrated review on the evidence that supports the reliance on cysteine of the kidney beyond cysteine antioxidant properties, highlighting the relevance of cysteine and its renal metabolism in the control of cysteine excess in the body as a pivotal source of metabolites to kidney biomass and bioenergetics and a promoter of adaptive responses to stressors. This view might translate into novel perspectives on the mechanisms of kidney function and blood pressure regulation and on clinical implications of the cysteine-related thiolome as a tool in precision medicine.

Expanding the Reactive Sulfur Metabolome: Intracellular and Efflux Measurements of Small Oxoacids of Sulfur (SOS) and H2S in Human Primary Vascular Cell Culture

Hydrogen sulfide (H2S) is an endogenous signaling molecule which is important for cardiovascular health, but its mechanism of action remains poorly understood. Here, we report measurements of H2S as well as its oxidized metabolites, termed small oxoacids of sulfur (SOS = HSOH and HOSOH), in four human primary vascular cell lines: smooth muscle and endothelial cells derived from both human arterial and coronary tissues. We use a methodology that targets small molecular weight sulfur species; mass spectrometric analysis allows for species quantification to report cellular concentrations based on an H2S calibration curve. The production of H2S and SOS is orders of magnitude higher in smooth muscle (nanomolar) as compared to endothelial cell lines (picomolar). In all the primary lines measured, the distributions of these three species were HOSOH >H2S > HSOH, with much higher SOS than seen previously in non-vascular cell lines. H2S and SOS were effluxed from smooth muscle cells in higher concentrations than endothelial cells. Aortic smooth muscle cells were used to examine changes under hypoxic growth conditions. Hypoxia caused notable increases in HSOH and ROS, which we attribute to enhanced sulfide quinone oxidase activity that results in reverse electron transport.

N-Acetylcysteine and Hydrogen Sulfide in Coronavirus Disease 2019

Significance: Hydrogen sulfide (H₂S) is one of the three main gasotransmitters that are endogenously produced in humans and are protective against oxidative stress. Recent findings from studies focusing on coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), shifted our attention to a potentially modulatory role of H₂S in this viral respiratory disease. Recent Advances: H₂S levels at hospital admission may be of importance since this gasotransmitter has been shown to be protective against lung damage through its antiviral, antioxidant, and anti-inflammatory actions. Furthermore, many COVID-19 cases have been described demonstrating remarkable clinical improvement upon administration of high doses of N-acetylcysteine (NAC). NAC is a renowned pharmacological antioxidant substance acting as a source of cysteine, thereby promoting endogenous glutathione (GSH) biosynthesis as well as generation of sulfane sulfur species when desulfurated to H₂S. Critical Issues: Combining H₂S physiology and currently available knowledge of COVID-19, H₂S is hypothesized to target three main vulnerabilities of SARS-CoV-2: (i) cell entry through interfering with functional host receptors, (ii) viral replication through acting on RNA-dependent RNA polymerase (RdRp), and (iii) the escalation of inflammation to a potentially lethal hyperinflammatory cytokine storm (toll-like receptor 4 [TLR4] pathway and NLR family pyrin domain containing 3 [NLRP3] inflammasome). Future Directions: Dissecting the breakdown of NAC reveals the possibility of increasing endogenous H₂S levels, which may provide a convenient rationale for the application of H₂S-targeted therapeutics. Further randomized-controlled trials are warranted to investigate its definitive role.

Sulfide metabolism and the mechanism of torpor

Hibernation is a powerful response of a number of mammalian species to reduce energy during the cold winter season, when food is scarce. Mammalian hibernators survive winter by spending most of the time in a state of torpor, where basal metabolic rate is strongly suppressed and body temperature comes closer to ambient temperature. These torpor bouts are regularly interrupted by short arousals, where metabolic rate and body temperature spontaneously return to normal levels. The mechanisms underlying these changes, and in particular the strong metabolic suppression of torpor, have long remained elusive. As summarized in this Commentary, increasing evidence points to a potential key role for hydrogen sulfide (H2S) in the suppression of mitochondrial respiration during torpor. The idea that H2S could be involved in hibernation originated in some early studies, where exogenous H2S gas was found to induce a torpor-like state in mice, and despite some controversy, the idea persisted. H2S is a widespread signaling molecule capable of inhibiting mitochondrial respiration in vitro and studies found significant in vivo changes in endogenous H2S metabolites associated with hibernation or torpor. Along with increased expression of H2S-synthesizing enzymes during torpor, H2S degradation catalyzed by the mitochondrial sulfide:quinone oxidoreductase (SQR) appears to have a key role in controlling H2S availability for inhibiting respiration. Specifically, in thirteen-lined squirrels, SQR is highly expressed and inhibited in torpor, possibly by acetylation, thereby limiting H2S oxidation and causing inhibition of respiration. H2S may also control other aspects associated with hibernation, such as synthesis of antioxidant enzymes and of SQR itself.

Hydrogen sulfide (H2S) - therapeutic relevance in rehabilitation and balneotherapy Systematic literature review and meta-analysis based on the PRISMA paradig

Background. An active molecule in sulfurous mineral - therapeutic waters and also in sapropelic mud is H2S, a hormetic gaseous molecule that can actively penetrate the skin. While high levels of H2S are extremely toxic, low levels are tolerated and have potential cytoprotective effects, with anti-inflammatory and antioxidant applications. Objective. This systematic review aims to rigorously select related articles and identify within their content the main possible uses of hydrogen sulfide from balneary sources and to explain its physiological mechanisms and therapeutic properties. Methods. To elaborate our systematic review, we have searched for relevant open access articles in 6 international databases: Cochrane , Elsevier , NCBI/PubMed , NCBI/PMC , PEDro , and ISI Web of Knowledge/Science , published from January 2016 until July 2021. The contextually quested keywords combinations/ syntaxes used are specified on this page. The eligible articles were analyzed in detail regarding pathologies addressed by hydrogen sulfide. All articles with any design (reviews, randomized controlled trials, non-randomized controlled trials, case-control studies, cross-sectional studies), if eligible according to the above-mentioned selection methodology, containing in the title the selected combinations, were included in the analysis. Articles were excluded in the second phase if they did not reach the relevance criterion. Results. Our search identified, first, 291 articles. After eliminating the duplicates and non-ISI articles, remained 121 papers. In the second phase, we applied a PEDro selection filter, resulting in 108 articles that passed the relevance criterion and were included in this systematic review. Conclusions. H2S biology and medical relevance are not fully understood and used adequately for sanogenic or medical purposes. More research is needed to fully understand the mechanisms and importance of this therapeutic gase. The link between balneotherapy and medical rehabilitation regarding the usage of hydrogen sulfide emphasises the unity for this medical speciality.

Cysteine Boosts Fitness Under Hypoxia-Mimicked Conditions in Ovarian Cancer by Metabolic Reprogramming

Among gynecologic malignancies, ovarian cancer is the third most prevalent and the most common cause of death, especially due to diagnosis at an advanced stage together with resistance to therapy. As a solid tumor grows, cancer cells in the microenvironment are exposed to regions of hypoxia, a selective pressure prompting tumor progression and chemoresistance. We have previously shown that cysteine contributes to the adaptation to this hypoxic microenvironment, but the mechanisms by which cysteine protects ovarian cancer cells from hypoxia-induced death are still to be unveiled. Herein, we hypothesized that cysteine contribution relies on cellular metabolism reprogramming and energy production, being cysteine itself a metabolic source. Our results strongly supported a role of xCT symporter in energy production that requires cysteine metabolism instead of hydrogen sulfide (H2S) per se. Cysteine degradation depends on the action of the H2S-synthesizing enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), and/or 3-mercaptopyruvate sulfurtransferase (MpST; together with cysteine aminotransferase, CAT). In normoxia, CBS and CSE inhibition had a mild impact on cysteine-sustained ATP production, pointing out the relevance of CAT + MpST pathway. However, in hypoxia, the concomitant inhibition of CBS and CSE had a stronger impact on ATP synthesis, thus also supporting a role of their hydrogen sulfide and/or cysteine persulfide-synthesizing activity in this stressful condition. However, the relative contributions of each of these enzymes (CBS/CSE/MpST) on cysteine-derived ATP synthesis under hypoxia remains unclear, due to the lack of specific inhibitors. Strikingly, NMR analysis strongly supported a role of cysteine in the whole cellular metabolism rewiring under hypoxia. Additionally, the use of cysteine to supply biosynthesis and bioenergetics was reinforced, bringing cysteine to the plateau of a main carbon sources in cancer. Collectively, this work supports that sulfur and carbon metabolism reprogramming underlies the adaptation to hypoxic microenvironment promoted by cysteine in ovarian cancer.

Protein disulfide isomerase inhibits endoplasmic reticulum stress response and apoptosis via its oxidoreductase activity in colorectal cancer

Protein disulfide isomerase (PDI), a principal endoplasmic reticulum resident oxidoreductase chaperone, is known to play a role in malignancies. This study aims to explore the molecular mechanism by which PDI regulates endoplasmic reticulum stress and the apoptosis signaling pathway in colorectal cancer (CRC). We determined the expression of PDI in CRC tissues and adjacent normal tissues. Gain- and loss- of function assays were conducted to evaluate the effects of PDI on oxidative stress, endoplasmic reticulum stress, and apoptosis in CRC cells, as reflected by hydrogen peroxide (H₂O₂) level and the expression of related proteins. PDI protein expression was upregulated in CRC tissues. Small molecule inhibitor of PDI or PDI knockdown reduced CRC cell viability and induced apoptosis. Overexpression of wild-type PDI augmented the viability of CRC cells and inhibited endoplasmic reticulum stress response and apoptosis. Small molecule inhibitor of PDI or PDI knockdown increased intracellular H₂O₂ level and activated apoptosis signaling pathway, which could be reversed by wild-type PDI restoration. Moreover, the catalytic active site of C-terminal of PDI was found to be indispensable for the regulatory effects of PDI on H₂O₂ levels, apoptosis and cell viability in CRC cells. Collectively, PDI inhibits endoplasmic reticulum stress and apoptosis of CRC cells through its oxidoreductase activity, thereby promoting the malignancy of CRC.

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.

Human METTL7B is an alkyl thiol methyltransferase that metabolizes hydrogen sulfide and captopril

Methylation of alkyl thiols is a biotransformation pathway designed to reduce thiol reactivity and potential toxicity, yet the gene and protein responsible for human alkyl thiol methyltransferase (TMT) activity remain unknown. Here we demonstrate with a range of experimental approaches using cell lines, in vitro systems, and recombinantly expressed enzyme, that human methyltransferase-like protein 7B (METTL7B) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine (AdoMet) to hydrogen sulfide (H2S) and other exogenous thiol small molecules. METTL7B gene modulation experiments, including knockdown in HepG2 cells and overexpression in HeLa cells, directly alter the methylation of the drug captopril, a historic probe substrate for TMT activity. Furthermore, recombinantly expressed and purified wild-type METTL7B methylates several thiol compounds, including H2S, 7α-thiospironolactone, L-penicillamine, and captopril, in a time- and concentration-dependent manner. Typical for AdoMet-dependent small molecule methyltransferases, S-adenosyl-L-homocysteine (AdoHcy) inhibited METTL7B activity in a competitive fashion. Similarly, mutating a conserved aspartate residue, proposed to anchor AdoMet into the active site, to an alanine (D98A) abolished methylation activity. Endogenous thiols such as glutathione and cysteine, or classic substrates for other known small molecule S-, N-, and O-methyltransferases, were not substrates for METTL7B. Our results confirm, for the first time, that METTL7B, a gene implicated in multiple disease states including rheumatoid arthritis and breast cancer, encodes a protein that methylates small molecule alkyl thiols. Identifying the catalytic function of METTL7B will enable future pharmacological research in disease pathophysiology where altered METTL7B expression and, potentially H2S levels, can disrupt cell growth and redox state.

Cysteine metabolic circuitries: druggable targets in cancer

To enable survival in adverse conditions, cancer cells undergo global metabolic adaptations. The amino acid cysteine actively contributes to cancer metabolic remodelling on three different levels: first, in its free form, in redox control, as a component of the antioxidant glutathione or its involvement in protein s-cysteinylation, a reversible post-translational modification; second, as a substrate for the production of hydrogen sulphide (H2S), which feeds the mitochondrial electron transfer chain and mediates per-sulphidation of ATPase and glycolytic enzymes, thereby stimulating cellular bioenergetics; and, finally, as a carbon source for epigenetic regulation, biomass production and energy production. This review will provide a systematic portrayal of the role of cysteine in cancer biology as a source of carbon and sulphur atoms, the pivotal role of cysteine in different metabolic pathways and the importance of H2S as an energetic substrate and signalling molecule. The different pools of cysteine in the cell and within the body, and their putative use as prognostic cancer markers will be also addressed. Finally, we will discuss the pharmacological means and potential of targeting cysteine metabolism for the treatment of cancer.

Hydrogen Sulfide, an Endogenous Stimulator of Mitochondrial Function in Cancer Cells

Hydrogen sulfide (H₂S) has a long history as toxic gas and environmental hazard; inhibition of cytochrome c oxidase (mitochondrial Complex IV) is viewed as a primary mode of its cytotoxic action. However, studies conducted over the last two decades unveiled multiple biological regulatory roles of H₂S as an endogenously produced mammalian gaseous transmitter. Cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST) are currently viewed as the principal mammalian H₂S-generating enzymes. In contrast to its inhibitory (toxicological) mitochondrial effects, at lower (physiological) concentrations, H₂S serves as a stimulator of electron transport in mammalian mitochondria, by acting as an electron donor—with sulfide:quinone oxidoreductase (SQR) being the immediate electron acceptor. The mitochondrial roles of H₂S are significant in various cancer cells, many of which exhibit high expression and partial mitochondrial localization of various H₂S producing enzymes. In addition to the stimulation of mitochondrial ATP production, the roles of endogenous H₂S in cancer cells include the maintenance of mitochondrial organization (protection against mitochondrial fission) and the maintenance of mitochondrial DNA repair (via the stimulation of the assembly of mitochondrial DNA repair complexes). The current article overviews the state-of-the-art knowledge regarding the mitochondrial functions of endogenously produced H₂S in cancer cells.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

The multifaceted roles of sulfane sulfur species in cancer-associated processes

Sulfane sulfur species comprise a variety of biologically relevant hydrogen sulfide (H₂S)-derived species, including per- and poly-sulfidated low molecular weight compounds and proteins. A growing body of evidence suggests that H₂S, currently recognized as a key signaling molecule in human physiology and pathophysiology, plays an important role in cancer biology by modulating cell bioenergetics and contributing to metabolic reprogramming. This is accomplished through functional modulation of target proteins via H₂S binding to heme iron centers or H₂S-mediated reversible per- or poly-sulfidation of specific cysteine residues. Since sulfane sulfur species are increasingly viewed not only as a major source of H₂S but also as key mediators of some of the biological effects commonly attributed to H₂S, the multifaceted role of these species in cancer biology is reviewed here with reference to H₂S, focusing on their metabolism, signaling function, impact on cell bioenergetics and anti-tumoral properties.

Emerging pharmacological tools to control hydrogen sulfide signaling in critical illness

Hydrogen sulfide (H2S) has long been known as a toxic environmental hazard. Discovery of physiological roles of H2S as a neurotransmitter by Kimura and colleagues triggered an intensive research in the biological roles of H2S in the past decades. Manipulation of H2S levels by inhibiting H2S synthesis or administration of H2S-releasing molecules revealed beneficial as well as harmful effects of H2S. As a result, it is now established that H2S levels are tightly controlled and too much or too little H2S levels cause harm. Nonetheless, translation of sulfide-based therapy to clinical practice has been stymied due to the very low therapeutic index of sulfide and the incomplete understanding of endogenous sulfide metabolism. One potential strategy to circumvent this problem is to use a safe and stable sulfide metabolite that may mediate effects of H2S. Alternatively, endogenous sulfide levels may be controlled using specific sulfide scavengers. In this review article, the role of endogenous H2S production and catabolism will be briefly reviewed followed by an introduction of thiosulfate and H2S scavengers as novel pharmacological tools to control H2S-dependent signaling.

Hydrogen Sulfide Metabolism and Signaling in the Tumor Microenvironment

Hydrogen sulfide (H2S), while historically perceived merely as a toxicant, has progressively emerged as a key regulator of numerous processes in mammalian physiology, exerting its signaling function essentially through interaction with and/or modification of proteins, targeting mainly cysteine residues and metal centers. As a gaseous signaling molecule that freely diffuses across aqueous and hydrophobic biological milieu, it has been designated the third 'gasotransmitter' in mammalian physiology. H2S is synthesized and detoxified by specialized endogenous enzymes that operate under a tight regulation, ensuring homeostatic levels of this otherwise toxic molecule. Indeed, imbalances in H2S levels associated with dysfunctional H2S metabolism have been growingly correlated with various human pathologies, from cardiovascular and neurodegenerative diseases to cancer. Several cancer cell lines and specimens have been shown to naturally overexpress one or more of the H2S-synthesizing enzymes. The resulting increased H2S levels have been proposed to promote cancer development through the regulation of various cancer-related processes, which led to the interest in pharmacological targeting of H2S metabolism. Herein are summarized some of the key observations that place H2S metabolism and signaling pathways at the forefront of the cellular mechanisms that support the establishment and development of a tumor within its complex and challenging microenvironment. Special emphasis is given to the mechanisms whereby H2S helps shaping cancer cell bioenergetic metabolism and affords resistance and adaptive mechanisms to hypoxia.

Hydrogen Sulfide: Emerging Role in Bladder, Kidney, and Prostate Malignancies

Hydrogen sulfide (H₂S) is the latest member of the gasotransmitter family and known to play essential roles in cancer pathophysiology. H₂S is produced endogenously and can be administered exogenously. Recent studies showed that H₂S in cancers has both pro- and antitumor roles. Understanding the difference in the expression and localization of tissue-specific H₂S-producing enzymes in healthy and cancer tissues allows us to develop tools for cancer diagnosis and treatment. Urological malignancies are some of the most common cancers in both men and women, and their early detection is vital since advanced cancers are recurrent, metastatic, and often resistant to treatment. This review summarizes the roles of H₂S in cancer and looks at current studies investigating H₂S activity and expression of H₂S-producing enzymes in urinary cancers. We specifically focused on urothelial carcinoma, renal cell carcinoma, and prostate cancer, as they form the majority of newly diagnosed urinary cancers. Recent studies show that besides the physiological activity of H₂S in cancer cells, there are patterns between the development and prognosis of urinary cancers and the expression of H₂S-producing enzymes and indirectly the H₂S levels. Though controversial and not completely understood, studying the expression of H₂S-producing enzymes in cancer tissue may represent an avenue for novel diagnostic and therapeutic strategies for addressing urological malignancies.

N-Acetylcysteine Serves as Substrate of 3-Mercaptopyruvate Sulfurtransferase and Stimulates Sulfide Metabolism in Colon Cancer Cells

Hydrogen sulfide (H₂S) is an endogenously produced signaling molecule. The enzymes 3-mercaptopyruvate sulfurtransferase (MST), partly localized in mitochondria, and the inner mitochondrial membrane-associated sulfide:quinone oxidoreductase (SQR), besides being respectively involved in the synthesis and catabolism of H₂S, generate sulfane sulfur species such as persulfides and polysulfides, currently recognized as mediating some of the H₂S biological effects. Reprogramming of H₂S metabolism was reported to support cellular proliferation and energy metabolism in cancer cells. As oxidative stress is a cancer hallmark and N-acetylcysteine (NAC) was recently suggested to act as an antioxidant by increasing intracellular levels of sulfane sulfur species, here we evaluated the effect of prolonged exposure to NAC on the H₂S metabolism of SW480 colon cancer cells. Cells exposed to NAC for 24 h displayed increased expression and activity of MST and SQR. Furthermore, NAC was shown to: (i) persist at detectable levels inside the cells exposed to the drug for up to 24 h and (ii) sustain H₂S synthesis by human MST more effectively than cysteine, as shown working on the isolated recombinant enzyme. We conclude that prolonged exposure of colon cancer cells to NAC stimulates H₂S metabolism and that NAC can serve as a substrate for human MST.