3-Mercaptopyruvate sulfurtransferase: an enzyme at the crossroads of sulfane sulfur trafficking

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

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

Structure and gene expression changes of the gill and liver in juvenile black porgy (Acanthopagrus schlegelii) under different salinities

Black porgy (Acanthopagrus schlegelii) is an important marine aquaculture species in China. It is an ideal object for the cultivation of low-salinity aquaculture strains in marine fish and the study of salinity tolerance mechanisms in fish because of its strong low-salinity tolerance ability. Gill is the main osmoregulatory organ in fish, and the liver plays an important role in the adaptation of the organism to stressful environments. In order to understand the coping mechanisms of the gills and livers of black porgy in different salinity environments, this study explored these organs after 30 days of culture in hypoosmotic (0.5 ppt), isosmotic (12 ppt), and normal seawater (28 ppt) at histologic, physiologic, and transcriptomic levels. The findings indicated that gill exhibited a higher number of differentially expressed genes than the liver, emphasizing the gill's heightened sensitivity to salinity changes. Protein interaction networks and enrichment analyses highlighted energy metabolism as a key regulatory focus at both 0.5 ppt and 12 ppt salinity in gills. Additionally, gills showed enrichment in ions, substance transport, and other metabolic pathways, suggesting a more direct regulatory response to salinity stress. The liver's regulatory patterns at different salinities exhibited significant distinctions, with pathways and genes related to metabolism, immunity, and antioxidants predominantly activated at 0.5 ppt, and molecular processes linked to cell proliferation taking precedence at 12 ppt salinity. Furthermore, the study revealed a reduction in the volume of the interlamellar cell mass (ILCM) of the gills, enhancing the contact area of the gill lamellae with water. At 0.5 ppt salinity, hepatic antioxidant enzyme activity increased, accompanied by oxidative stress damage. Conversely, at 12 ppt salinity, gill NKA activity significantly decreased without notable changes in liver structure. These results underscore the profound impact of salinity on gill structure and function, highlighting the crucial role of the liver in adapting to salinity environments.

Role of the 3-mercaptopyruvate sulfurtransferase in colon/colorectal cancers

The 3-mercaptopyruvate sulfurtransferase (MPST) is a protein persulfidase, occurring mainly in mitochondria. Although function of this protein in cancer cells has been already studied, no clear outcome can be postulated up to now. Therefore, we focused on the determination of function of MPST in colon (HCT116 cells)/colorectal (DLD1 cells) cancers. In silico analysis revealed that in gastrointestinal cancers, MPST together with its binding partners can be either of a high risk or might have a protective effect. Silencing of MPST gene resulted in decreased ATP, while acetyl-CoA levels were elevated. Increased apoptosis was detected in cells with silenced MPST gene, which was accompanied by decrease in mitochondrial membrane potential, but no changes in IP3 receptor's protein. Mitochondria underwent activation of fission and elevated DRP1 expression after MPST silencing. Proliferation and migration of DLD1 and HCT116 cells were markedly affected, showing the importance of MPST protein in colon/colorectal cancer development.

Ergothioneine boosts mitochondrial respiration and exercise performance via direct activation of MPST

Ergothioneine (EGT) is a diet-derived, atypical amino acid that accumulates to high levels in human tissues. Reduced EGT levels have been linked to age-related disorders, including neurodegenerative and cardiovascular diseases, while EGT supplementation is protective in a broad range of disease and aging models in mice. Despite these promising data, the direct and physiologically relevant molecular target of EGT has remained elusive. Here we use a systematic approach to identify how mitochondria remodel their metabolome in response to exercise training. From this data, we find that EGT accumulates in muscle mitochondria upon exercise training. Proteome-wide thermal stability studies identify 3-mercaptopyruvate sulfurtransferase (MPST) as a direct molecular target of EGT; EGT binds to and activates MPST, thereby boosting mitochondrial respiration and exercise training performance in mice. Together, these data identify the first physiologically relevant EGT target and establish the EGT-MPST axis as a molecular mechanism for regulating mitochondrial function and exercise performance.

Role of Hydrogen Sulfide in Oncological and Non-Oncological Disorders and Its Regulation by Non-Coding RNAs: A Comprehensive Review

Recently, myriad studies have defined the versatile abilities of gasotransmitters and their synthesizing enzymes to play a "Maestro" role in orchestrating several oncological and non-oncological circuits and, thus, nominated them as possible therapeutic targets. Although a significant amount of work has been conducted on the role of nitric oxide (NO) and carbon monoxide (CO) and their inter-relationship in the field of oncology, research about hydrogen sulfide (H2S) remains in its infancy. Recently, non-coding RNAs (ncRNAs) have been reported to play a dominating role in the regulation of the endogenous machinery system of H2S in several pathological contexts. A growing list of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are leading the way as upstream regulators for H2S biosynthesis in different mammalian cells during the development and progression of human diseases; therefore, their targeting can be of great therapeutic benefit. In the current review, the authors shed the light onto the biosynthetic pathways of H2S and their regulation by miRNAs and lncRNAs in various oncological and non-oncological disorders.

A link between energy metabolism and plant host adaptation states in the two-spotted spider mite, Tetranychus urticae (Koch)

Energy metabolism is a highly conserved process that balances generation of cellular energy and maintenance of redox homeostasis. It consists of five interconnected pathways: glycolysis, tricarboxylic acid cycle, pentose phosphate, trans-sulfuration, and NAD+ biosynthesis pathways. Environmental stress rewires cellular energy metabolism. Type-2 diabetes is a well-studied energy metabolism rewiring state in human pancreatic β-cells where glucose metabolism is uncoupled from insulin secretion. The two-spotted spider mite, Tetranychus urticae (Koch), exhibits a remarkable ability to adapt to environmental stress. Upon transfer to unfavourable plant hosts, mites experience extreme xenobiotic stress that dramatically affects their survivorship and fecundity. However, within 25 generations, mites adapt to the xenobiotic stress and restore their fitness. Mites' ability to withstand long-term xenobiotic stress raises a question of their energy metabolism states during host adaptation. Here, we compared the transcriptional responses of five energy metabolism pathways between host-adapted and non-adapted mites while using responses in human pancreatic islet donors to model these pathways under stress. We found that non-adapted mites and human pancreatic β-cells responded in a similar manner to host plant transfer and diabetogenic stress respectively, where redox homeostasis maintenance was favoured over energy generation. Remarkably, we found that upon host-adaptation, mite energy metabolic states were restored to normal. These findings suggest that genes involved in energy metabolism can serve as molecular markers for mite host-adaptation.

Effects of Cryptosporidium parvum infection on intestinal fungal microbiota in yaks (Bos grunniens)

During the last decade, researchers had started to focus on the relationship between intestinal parasitic infection and variation of intestinal microflora. Cryptosporidium is a widely known opportunistic and zoonotic pathogen. Several studies have shown that Cryptosporidium infection has impact to alter the gut microflora. However, there are only few studies referring to the fungal microflora changes in response to Cryptosporidium infection in highland ruminants. Therefore, the present study was performed for exploring the alternations of intestinal fungal microbiota in yaks after exposure to Cryptosporidium infection. In present study, Amplicon sequencing of ITS regions was used to study the variations of fungal microflora in yaks. After filtering the raw data, over 45 000 and 62 000 clean data were obtained in uninfected and infected yaks, respectively. By using alpha diversity analysis, it was found that there is no significant difference in the richness and evenness when positive samples were compared with negative ones, whereas intestinal fungal communities in different taxa in yaks were changed. The results of present study depicted that 2-phyla and 21-genera in the infected animals had significantly (P < 0.05) changed. These genera were Septoria, Coniothyrium, Cleistothelebolus, Bensingtonia, Cystobasidium, Filobasidium, Coprotus, Carex, Blumeria, Coprinellus, Leucosporidium, Phialophora, Isolepis, Ascobolus, Thecaphora, Mortierella, Urocystis, Symmetrospora and Lasiobolus. In addition, we found variations in 28 enzymes suggesting that the function of microbiota was also affected. It is concluded that there are drastic changes in the fungal microflora and microbiota functions after exposure to Cryptosporidium infection in yak. Our results help to focus on the prompt way for the development of new therapies to control Cryptosporidiosis.

Antibiotic Resistance: Challenges and Strategies in Combating Infections

From a broader perspective, antibiotic or antimicrobial resistance is still evolving and spreading internationally. Infectious diseases have become more complex and often impossible to cure, increasing morbidity and mortality. Despite the failure of conventional, standard antimicrobial therapy, no new class of antibiotics has been developed in the last 20 years, which results in various cutting-edge and other tactics that can be used to encounter these disease-causing microorganisms with antibiotic resistance. In the continued fight against bacterial infections, there is an urgent requirement for new antibiotics and other antimicrobials. Antibiotic resistance is inevitable, and pharmaceutical companies consistently show little interest in funding novel antibiotic research. Some methods are being used as a possible replacement for conventional antibiotics. Combination therapy, methods that target the proteins or enzymes that cause antimicrobial resistance and bacterial resistance, systems for delivery of the drug, physicochemical approaches, and informal ways, such as the CRISPR-Cas system, are some of these approaches. These various approaches influence how multi-drug-resistant organisms are handled in human clinical settings.

Regulation of Mitochondrial Respiration by Hydrogen Sulfide

Hydrogen sulfide (H2S), the third gasotransmitter, has positive roles in animals and plants. Mitochondria are the source and the target of H2S and the regulatory hub in metabolism, stress, and disease. Mitochondrial bioenergetics is a vital process that produces ATP and provides energy to support the physiological and biochemical processes. H2S regulates mitochondrial bioenergetic functions and mitochondrial oxidative phosphorylation. The article summarizes the recent knowledge of the chemical and biological characteristics, the mitochondrial biosynthesis of H2S, and the regulatory effects of H2S on the tricarboxylic acid cycle and the mitochondrial respiratory chain complexes. The roles of H2S on the tricarboxylic acid cycle and mitochondrial respiratory complexes in mammals have been widely studied. The biological function of H2S is now a hot topic in plants. Mitochondria are also vital organelles regulating plant processes. The regulation of H2S in plant mitochondrial functions is gaining more and more attention. This paper mainly summarizes the current knowledge on the regulatory effects of H2S on the tricarboxylic acid cycle (TCA) and the mitochondrial respiratory chain. A study of the roles of H2S in mitochondrial respiration in plants to elucidate the botanical function of H2S in plants would be highly desirable.

Gene co-expression network analysis for the selection of candidate early warning indicators of heat and nutrient stress in Posidonia oceanica

The continuous worldwide seagrasses decline calls for immediate actions in order to preserve this precious marine ecosystem. The main stressors that have been linked with decline in seagrasses are 1) the increasing ocean temperature due to climate change and 2) the continuous inputs of nutrients (eutrophication) associated with coastal human activities. To avoid the loss of seagrass populations, an "early warning" system is needed. We used Weighed Gene Co-expression Network Analysis (WGCNA), a systems biology approach, to identify potential candidate genes that can provide an early warning signal of stress in the Mediterranean iconic seagrass Posidonia oceanica, anticipating plant mortality. Plants were collected from both eutrophic (EU) and oligotrophic (OL) environments and were exposed to thermal and nutrient stress in a dedicated mesocosm. By correlating the whole-genome gene expression after 2-weeks exposure with the shoot survival percentage after 5-weeks exposure to stressors, we were able to identify several transcripts that indicated an early activation of several biological processes (BP) including: protein metabolic process, RNA metabolic process, organonitrogen compound biosynthetic process, catabolic process and response to stimulus, which were shared among OL and EU plants and among leaf and shoot apical meristem (SAM), in response to excessive heat and nutrients. Our results suggest a more dynamic and specific response of the SAM compared to the leaf, especially the SAM from plants coming from a stressful environment appeared more dynamic than the SAM from a pristine environment. A vast list of potential molecular markers is also provided that can be used as targets to assess field samples.

Rhodanese-Fold Containing Proteins in Humans: Not Just Key Players in Sulfur Trafficking

The Rhodanese-fold is a ubiquitous structural domain present in various protein subfamilies associated with different physiological functions or pathophysiological conditions in humans. Proteins harboring a Rhodanese domain are diverse in terms of domain architecture, with some representatives exhibiting one or several Rhodanese domains, fused or not to other structural domains. The most famous Rhodanese domains are catalytically active, thanks to an active-site loop containing an essential cysteine residue which allows for catalyzing sulfur transfer reactions involved in sulfur trafficking, hydrogen sulfide metabolism, biosynthesis of molybdenum cofactor, thio-modification of tRNAs or protein urmylation. In addition, they also catalyse phosphatase reactions linked to cell cycle regulation, and recent advances proposed a new role into tRNA hydroxylation, illustrating the catalytic versatility of Rhodanese domain. To date, no exhaustive analysis of Rhodanese containing protein equipment from humans is available. In this review, we focus on structural and biochemical properties of human-active Rhodanese-containing proteins, in order to provide a picture of their established or putative key roles in many essential biological functions.

3-Mercaptopyruvate sulfur transferase is a protein persulfidase

Protein S-persulfidation (P-SSH) is recognized as a common posttranslational modification. It occurs under basal conditions and is often observed to be elevated under stress conditions. However, the mechanism(s) by which proteins are persulfidated inside cells have remained unclear. Here we report that 3-mercaptopyruvate sulfur transferase (MPST) engages in direct protein-to-protein transpersulfidation reactions beyond its previously known protein substrates thioredoxin and MOCS3/Uba4, associated with H₂S generation and transfer RNA thiolation, respectively. We observe that depletion of MPST in human cells lowers overall intracellular protein persulfidation levels and identify a subset of proteins whose persulfidation depends on MPST. The predicted involvement of these proteins in the adaptation to stress responses supports the notion that MPST-dependent protein persulfidation promotes cytoprotective functions. The observation of MPST-independent protein persulfidation suggests that other protein persulfidases remain to be identified.

Hydrogen sulfide in the experimental models of arterial hypertension

Hydrogen sulfide (H₂S) is the third member of gasotransmitter family together with nitric oxide and carbon monoxide. H₂S is involved in the regulation of blood pressure by controlling vascular tone, sympathetic nervous system activity and renal sodium excretion. Moderate age-dependent hypertension and endothelial dysfunction develop in mice with knockout of cystathionine γ-lyase (CSE), the enzyme involved in H₂S production in the cardiovascular system. Decreased H₂S concentration as well as the expression and activities of H₂S-producing enzymes have been observed in most commonly used animal models of hypertension such as spontaneously hypertensive rats, Dahl salt-sensitive rats, chronic administration of NO synthase inhibitors, angiotensin II infusion and two-kidney-one-clip hypertension, the model of renovascular hypertension. Administration of H₂S donors decreases blood pressure in these models but has no major effects on blood pressure in normotensive animals. H₂S donors not only reduce blood pressure but also end-organ injury such as vascular and myocardial hypertrophy and remodeling, hypertension-associated kidney injury or erectile dysfunction. H₂S level and signaling are modulated by some antihypertensive medications as well as natural products with antihypertensive activity such as garlic polysulfides or plant-derived isothiocyanates as well as non-pharmacological interventions. Modifying H₂S signaling is the potential novel therapeutic approach for the management of hypertension, however, more experimental clinical studies about the role of H₂S in hypertension are required.

The Human Mercaptopyruvate Sulfurtransferase TUM1 Is Involved in Moco Biosynthesis, Cytosolic tRNA Thiolation and Cellular Bioenergetics in Human Embryonic Kidney Cells

Sulfur is an important element that is incorporated into many biomolecules in humans. The incorporation and transfer of sulfur into biomolecules is, however, facilitated by a series of different sulfurtransferases. Among these sulfurtransferases is the human mercaptopyruvate sulfurtransferase (MPST) also designated as tRNA thiouridine modification protein (TUM1). The role of the human TUM1 protein has been suggested in a wide range of physiological processes in the cell among which are but not limited to involvement in Molybdenum cofactor (Moco) biosynthesis, cytosolic tRNA thiolation and generation of H₂S as signaling molecule both in mitochondria and the cytosol. Previous interaction studies showed that TUM1 interacts with the L-cysteine desulfurase NFS1 and the Molybdenum cofactor biosynthesis protein 3 (MOCS3). Here, we show the roles of TUM1 in human cells using CRISPR/Cas9 genetically modified Human Embryonic Kidney cells. Here, we show that TUM1 is involved in the sulfur transfer for Molybdenum cofactor synthesis and tRNA thiomodification by spectrophotometric measurement of the activity of sulfite oxidase and liquid chromatography quantification of the level of sulfur-modified tRNA. Further, we show that TUM1 has a role in hydrogen sulfide production and cellular bioenergetics.

PRSS37 deficiency leads to impaired energy metabolism in testis and sperm revealed by DIA-based quantitative proteomic analysis

Our previous studies have reported that a putative trypsin-like serine protease, PRSS37, is exclusively expressed in testicular germ cells during late spermatogenesis and essential for sperm migration from the uterus into the oviduct and sperm-egg recognition via mediating the interaction between PDILT and ADAM3. In the present study, the global proteome profiles of wild-type (wt) and Prss37^-/- mice in testis and sperm were compared employing data independent acquisition (DIA) technology. Overall, 2506 and 459 differentially expressed proteins (DEPs) were identified in Prss37-null testis and sperm, respectively, when compared to control groups. Bioinformatic analyses revealed that most of DEPs were related to energy metabolism. Of note, the DEPs associated with pathways for the catabolism such as glucose via glycolysis, fatty acids via β-oxidation, and amino acids via oxidative deamination were significantly down-regulated. Meanwhile, the DEPs involved in the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation (OXPHOS) were remarkably decreased. The DIA data were further confirmed by a markedly reduction of intermediate metabolites (citrate and fumarate) in TCA cycle and terminal metabolite (ATP) in OXPHOS system after disruption of PRSS37. These outcomes not only provide a more comprehensive understanding of the male fertility of energy metabolism modulated by PRSS37 but also furnish a dynamic proteomic resource for further reproductive biology studies.

The Effects of Antioxidant Nutraceuticals on Cellular Sulfur Metabolism and Signaling

Significance: Nutraceuticals are ingested for health benefits, in addition to their general nutritional value. These dietary supplements have become increasingly popular since the late 20th century and they are a rapidly expanding global industry approaching a half-trillion U.S. dollars annually. Many nutraceuticals are promulgated as potent antioxidants. Recent Advances: Experimental support for the efficacy of nutraceuticals has lagged behind anecdotal exuberance. However, accumulating epidemiological evidence and recent, well-controlled clinical trials are beginning to support earlier animal and in vitro studies. Although still somewhat limited, encouraging results have been suggested in essentially all organ systems and against a wide range of pathophysiological conditions. Critical Issues: Health benefits of "antioxidant" nutraceuticals are largely attributed to their ability to scavenge oxidants. This has been criticized based on several factors, including limited bioavailability, short tissue retention time, and the preponderance of endogenous antioxidants. Recent attention has turned to nutraceutical activation of downstream antioxidant systems, especially the Keap1/Nrf2 (Kelch like ECH associated protein 1/nuclear factor erythroid 2-related factor 2) axis. The question now becomes, how do nutraceuticals activate this axis? Future Directions: Reactive sulfur species (RSS), including hydrogen sulfide (H2S) and its metabolites, are potent activators of the Keap1/Nrf2 axis and avid scavengers of reactive oxygen species. Evidence is beginning to accumulate that a variety of nutraceuticals increase cellular RSS by directly providing RSS in the diet, or through a number of catalytic mechanisms that increase endogenous RSS production. We propose that nutraceutical-specific targeting of RSS metabolism will lead to the design and development of even more efficacious antioxidant therapeutic strategies. Antioxid. Redox Signal. 38, 68-94.

Glioblastoma cell motility depends on enhanced oxidative stress coupled with mobilization of a sulfurtransferase

Cell motility is critical for tumor malignancy. Metabolism being an obligatory step in shaping cell behavior, we looked for metabolic weaknesses shared by motile cells across the diverse genetic contexts of patients' glioblastoma. Computational analyses of single-cell transcriptomes from thirty patients' tumors isolated cells with high motile potential and highlighted their metabolic specificities. These cells were characterized by enhanced mitochondrial load and oxidative stress coupled with mobilization of the cysteine metabolism enzyme 3-Mercaptopyruvate sulfurtransferase (MPST). Functional assays with patients' tumor-derived cells and -tissue organoids, and genetic and pharmacological manipulations confirmed that the cells depend on enhanced ROS production and MPST activity for their motility. MPST action involved protection of protein cysteine residues from damaging hyperoxidation. Its knockdown translated in reduced tumor burden, and a robust increase in mice survival. Starting from cell-by-cell analyses of the patients' tumors, our work unravels metabolic dependencies of cell malignancy maintained across heterogeneous genomic landscapes.

Glioblastoma cell motility depends on enhanced oxidative stress coupled with mobilization of a sulfurtransferase

Cell motility is critical for tumor malignancy. Metabolism being an obligatory step in shaping cell behavior, we looked for metabolic weaknesses shared by motile cells across the diverse genetic contexts of patients' glioblastoma. Computational analyses of single-cell transcriptomes from thirty patients' tumors isolated cells with high motile potential and highlighted their metabolic specificities. These cells were characterized by enhanced mitochondrial load and oxidative stress coupled with mobilization of the cysteine metabolism enzyme 3-Mercaptopyruvate sulfurtransferase (MPST). Functional assays with patients' tumor-derived cells and -tissue organoids, and genetic and pharmacological manipulations confirmed that the cells depend on enhanced ROS production and MPST activity for their motility. MPST action involved protection of protein cysteine residues from damaging hyperoxidation. Its knockdown translated in reduced tumor burden, and a robust increase in mice survival. Starting from cell-by-cell analyses of the patients' tumors, our work unravels metabolic dependencies of cell malignancy maintained across heterogeneous genomic landscapes.

Molecular Engines, Therapeutic Targets, and Challenges in Pediatric Brain Tumors: A Special Emphasis on Hydrogen Sulfide and RNA-Based Nano-Delivery

Pediatric primary brain tumors represent a real challenge in the oncology arena. Besides the psychosocial burden, brain tumors are considered one of the most difficult-to-treat malignancies due to their sophisticated cellular and molecular pathophysiology. Notwithstanding the advances in research and the substantial efforts to develop a suitable therapy, a full understanding of the molecular pathways involved in primary brain tumors is still demanded. On the other hand, the physiological nature of the blood-brain barrier (BBB) limits the efficiency of many available treatments, including molecular therapeutic approaches. Hydrogen Sulfide (H2S), as a member of the gasotransmitters family, and its synthesizing machinery have represented promising molecular targets for plentiful cancer types. However, its role in primary brain tumors, generally, and pediatric types, particularly, is barely investigated. In this review, the authors shed the light on the novel role of hydrogen sulfide (H2S) as a prominent player in pediatric brain tumor pathophysiology and its potential as a therapeutic avenue for brain tumors. In addition, the review also focuses on the challenges and opportunities of several molecular targeting approaches and proposes promising brain-delivery strategies for the sake of achieving better therapeutic results for brain tumor patients.

Function of gaseous hydrogen sulfide in liver fibrosis

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

Regulation of CyR61 expression and release by 3-mercaptopyruvate sulfurtransferase in colon cancer cells

Cysteine-rich angiogenic inducer 61 (CYR61, also termed CCN family member 1 or CCN1), is a matricellular protein encoded by the CYR61 gene. This protein has been implicated in the regulation of various cancer-associated processes including tumor growth, angiogenesis, tumor cell adhesion, migration, and invasion as well as the regulation of anticancer drug resistance. Hydrogen sulfide (H₂S) is a gaseous endogenous biological mediator, involved in the regulation of cellular bioenergetics, angiogenesis, invasion, and chemotherapeutic resistance in several types of cancer. H₂S is produced by three enzymes: cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current studies were set up to investigate if CBS or 3-MST regulates CyR61 in colon cancer cells in the context of the regulation of proliferation, migration, and survival. The study mainly utilized HCT116 cells, in which two of the principal H₂S-producing enzymes, CBS and 3-MST, are highly expressed. The H₂S donor GYY4137 and the polysulfide donor Na₂S₃ activated the CyR61 promoter in a concentration-dependent fashion. Aminooxyacetic acid (AOAA), a pharmacological inhibitor of CBS as well as HMPSNE: 2-[(4-hydroxy-6- methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one, a pharmacological inhibitor of 3-MST inhibited CyR61 mRNA expression. This effect was more pronounced in response to HMPSNE than to AOAA and occurred through the modulation of S1PR via ATF1 and CREB. CyR61 was found to play an active, but relatively minor role in maintaining colon cell proliferation. HMPSNE markedly suppressed the secretion/release of CyR61 from the colon cancer cells. Moreover, HMPSNE promoted colon cancer cell apoptosis; endogenously produced CyR61 was found to counteract this effect, at least in part via RhoA activation. Taken together, we conclude that the upregulation of 3-MST in cancer cells exerts cytoprotective effects and confers the cancer cells a more aggressive phenotype - at least in part via the modulation of CyR61 expression and release.

MPST deficiency promotes intestinal epithelial cell apoptosis and aggravates inflammatory bowel disease via AKT

Background & aims

Excessive inflammatory responses and oxidative stress are considered the main characteristics of inflammatory bowel disease (IBD). Endogenous hydrogen sulfide (H₂S) has been reported to show anti-inflammatory activity in IBD. The main aim of this study was to explore the role of 3-mercaptopyruvate sulfurtransferase (MPST), a key enzyme that regulates endogenous H₂S biosynthesis, in IBD.

Methods

Colonic MPST expression was evaluated in mice and patients with IBD. Various approaches were used to explore the concrete mechanism underlying MPST regulation of the progression of colitis through in vivo and in vitro models.

Results

MPST expression was markedly decreased in colonic samples from patients with ulcerative colitis (UC) or Crohn's disease (CD) and from mice treated with DSS. MPST deficiency significantly aggravated the symptoms of murine colitis, exacerbated inflammatory responses and apoptosis, and inhibited epithelium stem cell-derived organoid formation in an H₂S-independent manner. Consistently, when HT29 cells were treated with TNF-α, inhibition of MPST significantly increased the expression of proinflammatory cytokines, the amount of ROS and the prevalence of apoptosis, whereas overexpression of MPST markedly improved these effects. RNA-seq analysis showed that MPST might play a role in regulating apoptosis through AKT signaling. Mechanistically, MPST directly interacted with AKT and reduced the phosphorylation of AKT. Additionally, MPST expression was positively correlated with AKT expression in human IBD samples. In addition, overexpression of AKT rescued IEC apoptosis caused by MPST deficiency, while inhibition of AKT significantly aggravated it.

Conclusions

MPST protects the intestines from inflammation most likely by regulating the AKT/apoptosis axis in IECs. Our results may provide a novel therapeutic strategy for the treatment of colitis.

Sulfur incorporation into biomolecules: recent advances

Sulfur is an essential element for a variety of cellular constituents in all living organisms and adds considerable functionality to a wide range of biomolecules. The pathways for incorporating sulfur into central metabolites of the cell such as cysteine, methionine, cystathionine, and homocysteine have long been established. Furthermore, the importance of persulfide intermediates during the biosynthesis of thionucleotide-containing tRNAs, iron-sulfur clusters, thiamin diphosphate, and the molybdenum cofactor are well known. This review briefly surveys these topics while emphasizing more recent aspects of sulfur metabolism that involve unconventional biosynthetic pathways. Sacrificial sulfur transfers from protein cysteinyl side chains to precursors of thiamin and the nickel-pincer nucleotide (NPN) cofactor are described. Newer aspects of synthesis for lipoic acid, biotin, and other compounds are summarized, focusing on the requisite iron-sulfur cluster destruction. Sulfur transfers by using a noncore sulfide ligand bound to a [4Fe-4S] cluster are highlighted for generating certain thioamides and for alternative biosynthetic pathways of thionucleotides and the NPN cofactor. Thioamide formation by activating an amide oxygen atom via phosphorylation also is illustrated. The discussion of these topics stresses the chemical reaction mechanisms of the transformations and generally avoids comments on the gene/protein nomenclature or the sources of the enzymes. This work sets the stage for future efforts to decipher the diverse mechanisms of sulfur incorporation into biological molecules.

Possible molecular basis of the biochemical effects of cysteine-derived persulfides

Persulfides (RSSH/RSS⁻) are species closely related to thiols (RSH/RS⁻) and hydrogen sulfide (H₂S/HS⁻), and can be formed in biological systems in both low and high molecular weight cysteine-containing compounds. They are key intermediates in catabolic and biosynthetic processes, and have been proposed to participate in the transduction of hydrogen sulfide effects. Persulfides are acidic, more acidic than thiols, and the persulfide anions are expected to be the predominant species at neutral pH. The persulfide anion has high nucleophilicity, due in part to the alpha effect, i.e., the increased reactivity of a nucleophile when the neighboring atom has high electron density. In addition, persulfides have electrophilic character, a property that is absent in both thiols and hydrogen sulfide. In this article, the biochemistry of persulfides is described, and the possible ways in which the formation of a persulfide could impact on the properties of the biomolecule involved are discussed.

Role of the cystathionine β-synthase / H2S pathway in the development of cellular metabolic dysfunction and pseudohypoxia in down syndrome

BACKGROUND

Overexpression of the transsulfuration enzyme cystathionine-β-synthase (CBS), and overproduction of its product, hydrogen sulfide (H2S) are recognized as potential pathogenetic factors in Down syndrome (DS). The purpose of the study was to determine how the mitochondrial function and core metabolic pathways are affected by DS and how pharmacological inhibition of CBS affects these parameters.

METHODS

8 human control and 8 human DS fibroblast cell lines have been subjected to bioenergetic and fluxomic and proteomic analysis with and without treatment with a pharmacological inhibitor of CBS.

RESULTS

DS cells exhibited a significantly higher CBS expression than control cells, and produced more H2S. They also exhibited suppressed mitochondrial electron transport and oxygen consumption and suppressed Complex IV activity, impaired cell proliferation and increased ROS generation. Inhibition of H2S biosynthesis with aminooxyacetic acid reduced cellular H2S, improved cellular bioenergetics, attenuated ROS and improved proliferation. 13C glucose fluxomic analysis revealed that DS cells exhibit a suppression of the Krebs cycle activity with a compensatory increase in glycolysis. CBS inhibition restored the flux from glycolysis to the Krebs cycle and reactivated oxidative phosphorylation. Proteomic analysis revealed no CBS-dependent alterations in the expression level of the enzymes involved in glycolysis, oxidative phosphorylation and the pentose phosphate pathway. DS was associated with the dysregulation of several components of the autophagy network; CBS inhibition normalized several of these parameters.

CONCLUSIONS

Increased H2S generation in DS promotes pseudohypoxia and contributes to cellular metabolic dysfunction by causing a shift from oxidative phosphorylation to glycolysis.

Reactive sulfur species and their significance in health and disease

Reactive sulfur species (RSS) have been recognized in the last two decades as very important molecules in redox regulation. They are involved in metabolic processes and, in this way, they are responsible for maintenance of health. This review summarizes current information about the essential biological RSS, including H₂S, low molecular weight persulfides, protein persulfides as well as organic and inorganic polysulfides, their synthesis, catabolism and chemical reactivity. Moreover, the role of RSS disturbances in various pathologies including vascular diseases, chronic kidney diseases, diabetes mellitus Type 2, neurological diseases, obesity, chronic obstructive pulmonary disease and in the most current problem of COVID-19 is presented. The significance of RSS in aging is also mentioned. Finally, the possibilities of using the precursors of various forms of RSS for therapeutic purposes are discussed.

Antibiotic resistance: The challenges and some emerging strategies for tackling a global menace

Background

Antibiotic resistance is currently the most serious global threat to the effective treatment of bacterial infections. Antibiotic resistance has been established to adversely affect both clinical and therapeutic outcomes, with consequences ranging from treatment failures and the need for expensive and safer alternative drugs to the cost of higher rates of morbidity and mortality, longer hospitalization, and high‐healthcare costs. The search for new antibiotics and other antimicrobials continues to be a pressing need in humanity's battle against bacterial infections. Antibiotic resistance appears inevitable, and there is a continuous lack of interest in investing in new antibiotic research by pharmaceutical industries. This review summarized some new strategies for tackling antibiotic resistance in bacteria.

Methods

To provide an overview of the recent research, we look at some new strategies for preventing resistance and/or reviving bacteria's susceptibility to already existing antibiotics.

Results

Substantial pieces of evidence suggest that antimicrobials interact with host immunity, leading to potent indirect effects that improve antibacterial activities and may result in more swift and complete bactericidal effects. A new class of antibiotics referred to as immuno‐antibiotics and the targeting of some biochemical resistance pathway components including inhibition of SOS response and hydrogen sulfide as biochemical underlying networks of bacteria can be considered as new emerging strategies to combat antibiotic resistance in bacteria.

Conclusion

This review highlighted and discussed immuno‐antibiotics and inhibition of SOS response and hydrogen sulfide as biochemical underlying networks of bacteria as new weapons against antibiotic resistance in bacteria.

Commonly Used Alkylating Agents Limit Persulfide Detection by Converting Protein Persulfides into Thioethers

Protein persulfides (R‐S‐SH) have emerged as a common post‐translational modification. Detection and quantitation of protein persulfides requires trapping with alkylating agents. Here we show that alkylating agents differ dramatically in their ability to conserve the persulfide's sulfur–sulfur bond for subsequent detection by mass spectrometry. The two alkylating agents most commonly used in cell biology and biochemistry, N‐ethylmaleimide and iodoacetamide, are found to be unsuitable for the purpose of conserving persulfides under biologically relevant conditions. The resulting persulfide adducts (R‐S‐S‐Alk) rapidly convert into the corresponding thioethers (R‐S‐Alk) by donating sulfur to ambient nucleophilic acceptors. In contrast, certain other alkylating agents, in particular monobromobimane and N‐t‐butyl‐iodoacetamide, generate stable alkylated persulfides. We propose that the nature of the alkylating agent determines the ability of the disulfide bond (R‐S‐S‐Alk) to tautomerize into the thiosulfoxide (R‐(S=S)‐Alk), and/or the ability of nucleophiles to remove the sulfane sulfur atom from the thiosulfoxide.

MPST sulfurtransferase maintains mitochondrial protein import and cellular bioenergetics to attenuate obesity

Given the clinical, economic, and societal impact of obesity, unraveling the mechanisms of adipose tissue expansion remains of fundamental significance. We previously showed that white adipose tissue (WAT) levels of 3-mercaptopyruvate sulfurtransferase (MPST), a mitochondrial cysteine-catabolizing enzyme that yields pyruvate and sulfide species, are downregulated in obesity. Here, we report that Mpst deletion results in fat accumulation in mice fed a high-fat diet (HFD) through transcriptional and metabolic maladaptation. Mpst-deficient mice on HFD exhibit increased body weight and inguinal WAT mass, reduced metabolic rate, and impaired glucose/insulin tolerance. At the molecular level, Mpst ablation activates HIF1α, downregulates subunits of the translocase of outer/inner membrane (TIM/TOM) complex, and impairs mitochondrial protein import. MPST deficiency suppresses the TCA cycle, oxidative phosphorylation, and fatty acid oxidation, enhancing lipid accumulation. Sulfide donor administration to obese mice reverses the HFD-induced changes. These findings reveal the significance of MPST for white adipose tissue biology and metabolic health and identify a potential new therapeutic target for obesity.

Mitochondrial H2S Regulates BCAA Catabolism in Heart Failure

BACKGROUND

Hydrogen sulfide (H₂S) exerts mitochondria-specific actions that include the preservation of oxidative phosphorylation, biogenesis, and ATP synthesis, while inhibiting cell death. 3-MST (3-mercaptopyruvate sulfurtransferase) is a mitochondrial H₂S-producing enzyme whose functions in the cardiovascular disease are not fully understood. In the current study, we investigated the effects of global 3-MST deficiency in the setting of pressure overload-induced heart failure.

METHODS

Human myocardial samples obtained from patients with heart failure undergoing cardiac surgeries were probed for 3-MST protein expression. 3-MST knockout mice and C57BL/6J wild-type mice were subjected to transverse aortic constriction to induce pressure overload heart failure with reduced ejection fraction. Cardiac structure and function, vascular reactivity, exercise performance, mitochondrial respiration, and ATP synthesis efficiency were assessed. In addition, untargeted metabolomics were utilized to identify key pathways altered by 3-MST deficiency.

RESULTS

Myocardial 3-MST was significantly reduced in patients with heart failure compared with nonfailing controls. 3-MST KO mice exhibited increased accumulation of branched-chain amino acids in the myocardium, which was associated with reduced mitochondrial respiration and ATP synthesis, exacerbated cardiac and vascular dysfunction, and worsened exercise performance following transverse aortic constriction. Restoring myocardial branched-chain amino acid catabolism with 3,6-dichlorobenzo1[b]thiophene-2-carboxylic acid (BT2) and administration of a potent H₂S donor JK-1 ameliorates the detrimental effects of 3-MST deficiency in heart failure with reduced ejection fraction.

CONCLUSIONS

Our data suggest that 3-MST derived mitochondrial H₂S may play a regulatory role in branched-chain amino acid catabolism and mediate critical cardiovascular protection in heart failure.

Inhibition of the 3-mercaptopyruvate sulfurtransferase-hydrogen sulfide system promotes cellular lipid accumulation

H₂S is generated in the adipose tissue by cystathionine γ-lyase, cystathionine β-synthase, and 3-mercaptopyruvate sulfurtransferase (3-MST). H₂S plays multiple roles in the regulation of various metabolic processes, including insulin resistance. H₂S biosynthesis also occurs in adipocytes. Aging is known to be associated with a decline in H₂S. Therefore, the question arises whether endogenous H₂S deficiency may affect the process of adipocyte maturation and lipid accumulation. Among the three H₂S-generating enzymes, the role of 3-MST is the least understood in adipocytes. Here we tested the effect of the 3-MST inhibitor 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE) and the H₂S donor (GYY4137) on the differentiation and adipogenesis of the adipocyte-like cells 3T3-L1 in vitro. 3T3-L1 cells were differentiated into mature adipocytes in the presence of GYY4137 or HMPSNE. HMPSNE significantly enhanced lipid accumulation into the maturing adipocytes. On the other hand, suppressed lipid accumulation was observed in cells treated with the H₂S donor. 3-MST inhibition increased, while H₂S donation suppressed the expression of various H₂S-producing enzymes during adipocyte differentiation. 3-MST knockdown also facilitated adipocytic differentiation and lipid uptake. The underlying mechanisms may involve impairment of oxidative phosphorylation and fatty acid oxidation as well as the activation of various differentiation-associated transcription factors. Thus, the 3-MST/H₂S system plays a tonic role in suppressing lipid accumulation and limiting the differentiation of adipocytes. Stimulation of 3-MST activity or supplementation of H₂S—which has been recently linked to various experimental therapeutic approaches during aging—may be a potential experimental approach to counteract adipogenesis.

Emerging roles of cystathionine β-synthase in various forms of cancer

The expression of the reverse transsulfuration enzyme cystathionine-β-synthase (CBS) is markedly increased in many forms of cancer, including colorectal, ovarian, lung, breast and kidney, while in other cancers (liver cancer and glioma) it becomes downregulated. According to the clinical database data in high-CBS-expressor cancers (e.g. colon or ovarian cancer), high CBS expression typically predicts lower survival, while in the low-CBS-expressor cancers (e.g. liver cancer), low CBS expression is associated with lower survival. In the high-CBS expressing tumor cells, CBS, and its product hydrogen sulfide (H₂S) serves as a bioenergetic, proliferative, cytoprotective and stemness factor; it also supports angiogenesis and epithelial-to-mesenchymal transition in the cancer microenvironment. The current article reviews the various tumor-cell-supporting roles of the CBS/H₂S axis in high-CBS expressor cancers and overviews the anticancer effects of CBS silencing and pharmacological CBS inhibition in various cancer models in vitro and in vivo; it also outlines potential approaches for biomarker identification, to support future targeted cancer therapies based on pharmacological CBS inhibition.

Heart and kidney H2S production is reduced in hypertensive and older rats

The prevalence of hypertension increases with age, but the mechanisms linking this phenomenon are not well understood. Hydrogen sulfide (H₂S) may be involved in this process, as it plays a role in the cardiovascular system, affecting blood pressure and heart and kidney functions. The aim of this study was to evaluate the influence of hypertension and aging on sulfur-containing compounds metabolism in the hearts and kidneys of Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR) of different age groups. We determined the expression and activity of four enzymes participating in H₂S production: cystathionine beta-synthase (CBS), cystathionine gamma-lyase (CTH), 3-mercaptopyruvate sulfurtransferase (MPST), and thiosulfate sulfurtransferase (TST). The levels of reduced/oxidized glutathione, cysteine, cystine, and cystathionine, and the ability of tissues to form hydrogen sulfide were also investigated. Tissues obtained from younger WKY rats produced the highest amounts of H₂S. The effect of hypertension on the metabolism of sulfur-containing compounds was manifested by a decrease in sulfane sulfur concentrations in heart homogenates and a decrease in CTH activity in the kidneys. The hearts and kidneys of older WKY rats were characterized by lower MPST or CTH gene expression, respectively, compared to younger animals. Our study demonstrates that hypertension and aging influence cardiac and renal sulfur-containing compounds metabolism and reduce H₂S production. Furthermore, we showed that MPST plays a major role in the production of hydrogen sulfide in the heart and CTH in the kidneys of rats.

Hydrogen sulfide-induced post-translational modification as a potential drug target

Hydrogen sulfide (H₂S) is one of the three known gas signal transducers, and since its potential physiological role was reported, the literature on H₂S has been increasing. H₂S is involved in processes such as vasodilation, neurotransmission, angiogenesis, inflammation, and the prevention of ischemia-reperfusion injury, and its mechanism remains to be further studied. At present, the role of post-translational processing of proteins has been considered as a possible mechanism for the involvement of H₂S in a variety of physiological processes. Current studies have shown that H₂S is involved in S-sulfhydration, phosphorylation, and S-nitrosylation of proteins, etc. This paper focuses on the effects of protein modification involving H₂S on physiological and pathological processes, looking forward to providing guidance for subsequent research.

Hydrogen sulphide in liver glucose/lipid metabolism and non-alcoholic fatty liver disease

BACKGROUND

For a long time, hydrogen sulphide (H₂ S) was considered only as a toxic gas, inhibiting mitochondrial respiration at the level of cytochrome c oxidase, and an environmental pollutant. Nowadays, H₂ S is recognized as the third mammalian gasotransmitter, playing an important role in inflammation, septic shock, ischaemia reperfusion events, cardiovascular disease and more recently in liver physiology and chronic liver diseases such as non-alcoholic fatty liver disease (NAFLD).

METHODS

This narrative review is based on literature search using PubMed.

RESULTS

From a bioenergetic perspective, H₂ S is a very unique molecule, serving as a mitochondrial poison at high concentrations or as an inorganic mitochondrial substrate at low concentrations. By using transgenic animal models to specifically modulate liver H₂ S biosynthesis or exogenous compounds that release H₂ S, several studies demonstrated that H₂ S is a key player in liver glucose and lipid metabolism. Liver H₂ S content and biosynthesis were also altered in NAFLD animal models with the in vivo administration of H₂ S-releasing molecules preventing the further escalation into non-alcoholic-steatohepatitis. Liver steady-state levels of H₂ S, and hence its cell signalling properties, are controlled by a tight balance between its biosynthesis, mainly through the transsulphuration pathway, and its mitochondrial oxidation via the sulphide oxidizing unit. However, studies investigating mitochondrial H₂ S oxidation in liver dysfunction still remain scarce.

CONCLUSIONS

Since H₂ S emerges as a key regulator of liver metabolism and metabolic flexibility, further understanding the physiological relevance of mitochondrial H₂ S oxidation in liver energy homeostasis and its potential implication in chronic liver diseases are of great interest.

A fluorescent probe derived from Berberrubine for detecting hydrogen polysulfide in food samples

In this work, we chose the fluorophore Berberrubine to develop a selective probe for hydrogen polysulfide (H₂S_n), and applied it into the detection in both food samples and living cells. The developed probe, HER9SS, suggested practical steadiness and serviceability, especially for multi-scene detection. The detecting system was stable in relatively wide pH (7.0-11.0) and temperature (25-45 °C) ranges. Both the storage of BER9SS in solid or in solution could maintain the steadiness over 7 d. BER9SS also indicated advantages including rapid response (within 15 min), high sensitivity (LOD = 0.02 μM; LOQ = 0.01 μM), long linear range (0-15.0 equivalent) and high selectivity among competing analytes. The recovery ranging in 95.23% - 104.8% in the applications in food sources samples (including water and plants) and food samples inferred the practical potential of BER9SS. In biological imaging, BER9SS could achieve both the dose-dependent monitoring and the β-lapachone-induced generation of H₂S_n. Therefore, the information in this work might be useful for the development of fluorescent probes from natural products for multi-scene applications in future, especially with the corresponding attentions on the practicability and serviceability.

Sulfane Sulfur Compounds as Source of Reappearance of Reductive Off-Odors in Wine

Reactive compounds with one or more sulfane sulfur atoms can be an important source of reductive off-odors in wine. These substances contain labile sulfur, which can participate in microbiological (enzymatic) and chemical transformations (including in the post-bottling period), releasing malodorous hydrogen sulfide (H2S) and its derivatives (MeSH, EtSH, etc.). The following sulfane sulfur compounds were considered in this review as important precursors in the wine chemistry of reductive aromas: elemental sulfur (S8), persulfides (R-S-S-H), polysulfanes (R-Sn-R(′)), polythionates (−O3S-Sn-SO3−), thiosulfate (S2O32−) and derivatives of (poly)sulfane monosulfonic acids (R-Sn-SO3H). This review discusses the formation of these compounds, their reactivity and chemical transformations in wine, including reactions of nucleophilic substitution. In particular, the reactions of thiolysis, thiosulfatolysis and sulfitolysis of sulfane sulfur compounds are described, which lead in the end to reductive aroma compounds. In this way, the review attempts to shed light on some of the mysteries in the field of sulfur chemistry in wine and the reappearance of reductive off-odors after bottling.

Sulfurtransferases and Cystathionine Beta-Synthase Expression in Different Human Leukemia Cell Lines

The studies concerned the expression of sulfurtransferases and cystathionine beta-synthase in six human leukemia cell lines: B cell acute lymphoblastic leukemia-B-ALL (REH cells), T cell acute lymphoblastic leukemia-T-ALL (DND-41 and MOLT-4 cells), acute myeloid leukemia—AML (MV4-11 and MOLM-14 cells), and chronic myeloid leukemia—CML (K562 cells). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis were performed to determine the expression of thiosulfate sulfurtransferase, 3-mercaptopyruvate sulfurtransferase, gamma-cystathionase, and cystathionine beta-synthase on the mRNA and protein level. Interestingly, we found significant differences in the mRNA and protein levels of sulfurtransferases and cystathionine beta-synthase in the studied leukemia cells. The obtained results may contribute to elucidating the significance of the differences between the studied cells in the field of sulfur compound metabolism and finding new promising ways to inhibit the proliferation of various types of leukemic cells by modulating the activity of sulfurtransferases, cystathionine beta-synthase, and, consequently, the change of intracellular level of sulfane sulfur as well as H₂S and reactive oxygen species production.

Sulfur Administration in Fe-S Cluster Homeostasis

Mitochondria are the key organelles of Fe–S cluster synthesis. They contain the enzyme cysteine desulfurase, a scaffold protein, iron and electron donors, and specific chaperons all required for the formation of Fe–S clusters. The newly formed cluster can be utilized by mitochondrial Fe–S protein synthesis or undergo further transformation. Mitochondrial Fe–S cluster biogenesis components are required in the cytosolic iron–sulfur cluster assembly machinery for cytosolic and nuclear cluster supplies. Clusters that are the key components of Fe–S proteins are vulnerable and prone to degradation whenever exposed to oxidative stress. However, once degraded, the Fe–S cluster can be resynthesized or repaired. It has been proposed that sulfurtransferases, rhodanese, and 3-mercaptopyruvate sulfurtransferase, responsible for sulfur transfer from donor to nucleophilic acceptor, are involved in the Fe–S cluster formation, maturation, or reconstitution. In the present paper, we attempt to sum up our knowledge on the involvement of sulfurtransferases not only in sulfur administration but also in the Fe–S cluster formation in mammals and yeasts, and on reconstitution-damaged cluster or restoration of enzyme’s attenuated activity.

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known (‘classic’) toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a ‘classical’ mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

Novel Aryl-Substituted Pyrimidones as Inhibitors of 3-Mercaptopyruvate Sulfurtransferase with Antiproliferative Efficacy in Colon Cancer

The enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) is one of the more recently identified mammalian sources of H₂S. A recent study identified several novel 3-MST inhibitors with micromolar potency. Among those, (2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one) or HMPSNE was found to be the most potent and selective. We now took the central core of this compound and modified the pyrimidone and the arylketone sides independently. A 63-compound library was synthesized; compounds were tested for H₂S generation from recombinant 3-MST in vitro. Active compounds were subsequently tested to elucidate their potency and selectivity. Computer modeling studies have delineated some of the key structural features necessary for binding to the 3-MST's active site. Six novel 3-MST inhibitors were tested in cell-based assays: they exerted inhibitory effects in murine MC38 and CT26 colon cancer cell proliferation; the antiproliferative effect of the compound with the highest potency and best cell-based activity (1b) was also confirmed on the growth of MC38 tumors in mice.

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.