Glutathione Degradation

Gamma-glutamyl transferase 5 overexpression in cerebrovascular endothelial cells improves brain pathology, cognition, and behavior in APP/PS1 mice

JOURNAL/nrgr/04.03/01300535-202502000-00030/figure1/v/2024-05-28T214302Z/r/image-tiff In patients with Alzheimer's disease, gamma-glutamyl transferase 5 (GGT5) expression has been observed to be downregulated in cerebrovascular endothelial cells. However, the functional role of GGT5 in the development of Alzheimer's disease remains unclear. This study aimed to explore the effect of GGT5 on cognitive function and brain pathology in an APP/PS1 mouse model of Alzheimer's disease, as well as the underlying mechanism. We observed a significant reduction in GGT5 expression in two in vitro models of Alzheimer's disease (Aβ1-42-treated hCMEC/D3 and bEnd.3 cells), as well as in the APP/PS1 mouse model. Additionally, injection of APP/PS1 mice with an adeno-associated virus encoding GGT5 enhanced hippocampal synaptic plasticity and mitigated cognitive deficits. Interestingly, increasing GGT5 expression in cerebrovascular endothelial cells reduced levels of both soluble and insoluble amyloid-β in the brains of APP/PS1 mice. This effect may be attributable to inhibition of the expression of β-site APP cleaving enzyme 1, which is mediated by nuclear factor-kappa B. Our findings demonstrate that GGT5 expression in cerebrovascular endothelial cells is inversely associated with Alzheimer's disease pathogenesis, and that GGT5 upregulation mitigates cognitive deficits in APP/PS1 mice. These findings suggest that GGT5 expression in cerebrovascular endothelial cells is a potential therapeutic target and biomarker for Alzheimer's disease.

Glutathione‑degrading enzymes in the complex landscape of tumors (Review)

Glutathione (GSH)‑degrading enzymes are essential for starting the first stages of GSH degradation. These enzymes include extracellular γ‑glutamyl transpeptidase (GGT) and intracellular GSH‑specific γ‑glutamylcyclotransferase 1 (ChaC1) and 2. These enzymes are essential for cellular activities, such as immune response, differentiation, proliferation, homeostasis regulation and programmed cell death. Tumor tissue frequently exhibits abnormal expression of GSH‑degrading enzymes, which has a key impact on the development and spread of malignancies. The present review summarizes gene and protein structure, catalytic activity and regulation of GSH‑degrading enzymes, their vital roles in tumor development (including regulation of oxidative and endoplasmic reticulum stress, control of programmed cell death, promotion of inflammation and tumorigenesis and modulation of drug resistance in tumor cells) and potential role as diagnostic biomarkers and therapeutic targets.

GSH and Ferroptosis: Side-by-Side Partners in the Fight against Tumors

Glutathione (GSH), a prominent antioxidant in organisms, exhibits diverse biological functions and is crucial in safeguarding cells against oxidative harm and upholding a stable redox milieu. The metabolism of GSH is implicated in numerous diseases, particularly in the progression of malignant tumors. Consequently, therapeutic strategies targeting the regulation of GSH synthesis and metabolism to modulate GSH levels represent a promising avenue for future research. This study aimed to elucidate the intricate relationship between GSH metabolism and ferroptosis, highlighting how modulation of GSH metabolism can impact cellular susceptibility to ferroptosis and consequently influence the development of tumors and other diseases. The paper provides a comprehensive overview of the physiological functions of GSH, including its structural characteristics, physicochemical properties, sources, and metabolic pathways, as well as investigate the molecular mechanisms underlying GSH regulation of ferroptosis and potential therapeutic interventions. Unraveling the biological role of GSH holds promise for individuals afflicted with tumors.

Transcriptomic investigation and biomarker discovery for zinc response in oysters Crassostrea gasar

In an era of unprecedented industrial and agricultural growth, metal contamination in marine environments is a pressing concern. Sentinel organisms such as the mangrove oyster Crassostrea gasar provide valuable insights into these environments' health. However, a comprehensive understanding of the molecular mechanisms underlying their response to metal exposure remains elusive. To address this gap, we reanalyzed the 454-sequencing data of C. gasar, utilizing an array of bioinformatics workflow of CDTA (Combined De Novo Transcriptome Assembly) to generate a more representative assembly. In parallel, C. gasar individuals were exposed to two concentrations of zinc (850 and 4500 μg L-1 Zn) for 48 h to understand their molecular responses. We utilized Trinotate workflow for the 11,684-CDTA unigenes annotation, with most transcripts aligning with the genus Crassostrea. Our analysis indicated that 67.3% of transcript sequences showed homology with Pfam, while 51.4% and 54.5%, respectively had GO and KO terms annotated. We identified potential metal pollution biomarkers, focusing on metal-related genes, such as those related to the GSH biosynthesis (CHAC1 and GCLC-like), to zinc transporters (ZNT2-like), and metallothionein (MT-like). The evolutionary conservation of these genes within the Crassostrea genus was assessed through phylogenetic analysis. Further, these genes were evaluated by qPCR in the laboratory exposed oysters. All target genes exhibited significant upregulation upon exposure to Zn at both 850 and 4500 μg L-1, except for GCLC-like, which showed upregulation only at the higher concentration of 4500 μg L-1. This result suggests distinct activation thresholds and complex interactions among these genes in response to varying Zn concentrations. Our study provides insights into the molecular responses of C. gasar to Zn, adding valuable tools for monitoring metal pollution in marine ecosystems using the mangrove oyster as a sentinel organism.

N2-Acetylornithine deacetylase functions as a Cys-Gly dipeptidase in the cytosolic glutathione degradation pathway in Arabidopsis thaliana

Glutathione (GSH) is required for various physiological processes in plants, including redox regulation and detoxification of harmful compounds. GSH also functions as a repository for assimilated sulfur and is actively catabolized in plants. In Arabidopsis, GSH is mainly degraded initially by cytosolic enzymes, γ-glutamyl cyclotransferase, and γ-glutamyl peptidase, which release cysteinylglycine (Cys-Gly). However, the subsequent enzyme responsible for catabolizing this dipeptide has not been identified to date. In the present study, we identified At4g17830 as a Cys-Gly dipeptidase, namely cysteinylglycine peptidase 1 (CGP1). CGP1 complemented the phenotype of the yeast mutant that cannot degrade Cys-Gly. The Arabidopsis cgp1 mutant had lower Cys-Gly degradation activity than the wild type and showed perturbed concentrations of thiol compounds. Recombinant CGP1 showed reasonable Cys-Gly degradation activity in vitro. Metabolomic analysis revealed that cgp1 exhibited signs of severe sulfur deficiency, such as elevated accumulation of O-acetylserine (OAS) and the decrease in sulfur-containing metabolites. Morphological changes observed in cgp1, including longer primary roots of germinating seeds, were also likely associated with sulfur starvation. Notably, At4g17830 has previously been reported to encode an N2-acetylornithine deacetylase (NAOD) that functions in the ornithine biosynthesis. The cgp1 mutant did not show a decrease in ornithine content, whereas the analysis of CGP1 structure did not rule out the possibility that CGP1 has Cys-Gly dipeptidase and NAOD activities. Therefore, we propose that CGP1 is a Cys-Gly dipeptidase that functions in the cytosolic GSH degradation pathway and may play dual roles in GSH and ornithine metabolism.

The Emerging Roles of γ-Glutamyl Peptides Produced by γ-Glutamyltransferase and the Glutathione Synthesis System

L-γ-Glutamyl-L-cysteinyl-glycine is commonly referred to as glutathione (GSH); this ubiquitous thiol plays essential roles in animal life. Conjugation and electron donation to enzymes such as glutathione peroxidase (GPX) are prominent functions of GSH. Cellular glutathione balance is robustly maintained via regulated synthesis, which is catalyzed via the coordination of γ-glutamyl-cysteine synthetase (γ-GCS) and glutathione synthetase, as well as by reductive recycling by glutathione reductase. A prevailing short supply of L-cysteine (Cys) tends to limit glutathione synthesis, which leads to the production of various other γ-glutamyl peptides due to the unique enzymatic properties of γ-GCS. Extracellular degradation of glutathione by γ-glutamyltransferase (GGT) is a dominant source of Cys for some cells. GGT catalyzes the hydrolytic removal of the γ-glutamyl group of glutathione or transfers it to amino acids or to dipeptides outside cells. Such processes depend on an abundance of acceptor substrates. However, the physiological roles of extracellularly preserved γ-glutamyl peptides have long been unclear. The identification of γ-glutamyl peptides, such as glutathione, as allosteric modulators of calcium-sensing receptors (CaSRs) could provide insights into the significance of the preservation of γ-glutamyl peptides. It is conceivable that GGT could generate a new class of intercellular messaging molecules in response to extracellular microenvironments.

A novel nomogram based on GD for predicting prognosis in hepatocellular carcinoma

Purpose

The prognosis of liver cancer remains unfavorable nowadays, making the search for predictive biomarkers of liver cancer prognosis of paramount importance to guide clinical diagnosis and treatment. This study was conducted to explore more prognostic markers for most HCC.

Patients and methods

A total of 330 patients were enrolled in this study according to the inclusion and exclusion criteria. Follow-up data were collected for all patients until the cutoff date of the study, February 2023. In addition, patient outcomes were assessed with progression-free survival (PFS) and overall survival (OS). All statistical analysis was conducted using R 4.2.0 software.

Results

Univariate analysis illustrated that the GD [the product of gamma-glutamyl transpeptidase (GGT) concentration and D-dimer concentration, GD=GGT*D-dimer] levels were related to PFS (p<0.05) and OS (p<0.05). Kaplan-Meier survival curves and log-rank tests indicated a significant difference among different levels of GD (p<0.001). Multivariate analysis demonstrated GD as an independent prognostic factor for HCC. The C-indexes of nomogram were 0.77 and 0.76 in the training or validation cohort, respectively. Area Under the Curve (AUC) of 1-, 2-, 3-, and 4-year OS showed satisfactory accuracy, and the calibration curve illustrated brilliant consistence between the ideal and predicted values.

Conclusions

Herein, it was demonstrated that GD was an independent prognostic factor for HCC and revealed the potential to predict the PFS and OS in patients with HCC. Moreover, the nomogram based on GD illustrated a satisfactory prediction ability in comparison to other models without GD.

Cystine/glutamate antiporter System xc- deficiency impairs insulin secretion in mice

AIMS/HYPOTHESIS

Glutamate-induced cytotoxicity (excitotoxicity) has been detected in pancreatic beta cells. The cystine/glutamate antiporter System xc- exports glutamate to the extracellular space and is therefore implicated as driving excitotoxicity. As of yet, it has not been investigated whether System xc- contributes to pancreatic islet function.

METHODS

This study describes the implications of deficiency of System xc- on glucose metabolism in both constitutive and myeloid cell-specific knockout mice using metabolic tests and diet-induced obesity. Pancreatic islets were isolated and analysed for beta cell function, glutathione levels and ER stress.

RESULTS

Constitutive System xc- deficiency led to an approximately threefold decrease in glutathione levels in the pancreatic islets as well as cystine shortage characterised by upregulation of Chac1. This shortage further manifested as downregulation of beta cell identity genes and a tonic increase in endoplasmic reticulum stress markers, which resulted in diminished insulin secretion both in vitro and in vivo. Myeloid-specific deletion did not have a significant impact on metabolism or islet function.

CONCLUSIONS/INTERPRETATION

These findings suggest that System xc- is required for glutathione maintenance and insulin production in beta cells and that the system is dispensable for islet macrophage function.

The kinetics of glutathione in the gastrointestinal tract of weaned piglets supplemented with different doses of dietary reduced glutathione

This study aimed to investigate the kinetics of dietary GSH in the gastrointestinal tract and the effect of GSH on the intestinal redox status of weaned piglets. Forty-eight piglets with an average age of 26 days and an average body weight of 7.7 kg were used in this study. The piglets were divided into three treatment groups including the control group with a basal diet (CON) and two GSH groups with a basal diet supplemented with 0.1% GSH (LGSH) and 1.0% GSH (HGSH), respectively. The basal diet did not contain any GSH. The experiment lasted for 14 days, with eight animals sampled from each group on d5 and 14. The parts of 0-5%, 5-75%, and 75-100% of the length of the small intestine were assigned to SI1, SI2, and SI3. The results showed that GSH almost completely disappeared from the digesta at SI2. However, no difference in the GSH level in mucosa, liver, and blood erythrocytes was found. The level of cysteine (CYS) in SI1 digesta was significantly higher in HGSH than CON and LGSH on d14, and similar findings were observed for cystine (CYSS) in SI3 digesta on d5. The CYSS level in HGSH was also significantly higher than LGSH in the stomach on d14, while no CYS or CYSS was detected in the stomach for control animals, indicating the breakdown of GSH to CYS already occurred in the stomach. Irrespective of the dietary treatment, the CYS level on d14 and the CYSS level on d5 and 14 were increased when moving more distally into the gastrointestinal tract. Furthermore, the mucosal CYS level was significantly increased at SI1 in the LGSH and HGSH group compared with CON on d5. Glutathione disulfide (GSSG) was recovered in the diets and digesta from the LGSH and HGSH group, which could demonstrate the auto-oxidation of GSH. It is, therefore, concluded that GSH supplementation could not increase the small intestinal mucosal GSH level of weaned piglets, and this could potentially relate to the kinetics of GSH in the digestive tract, where GSH seemed to be prone to the breakdown to CYS and CYSS and the auto-oxidation to GSSG.

Intermittent dietary methionine deprivation facilitates tumoral ferroptosis and synergizes with checkpoint blockade

Dietary methionine interventions are beneficial to apoptosis-inducing chemotherapy and radiotherapy for cancer, while their effects on ferroptosis-targeting therapy and immunotherapy are unknown. Here we show the length of time methionine deprivation affects tumoral ferroptosis differently. Prolonged methionine deprivation prevents glutathione (GSH) depletion from exceeding the death threshold by blocking cation transport regulator homolog 1 (CHAC1) protein synthesis. Whereas, short-term methionine starvation accelerates ferroptosis by stimulating CHAC1 transcription. In vivo, dietary methionine with intermittent but not sustained deprivation augments tumoral ferroptosis. Intermittent methionine deprivation also sensitizes tumor cells against CD8+ T cell-mediated cytotoxicity and synergize checkpoint blockade therapy by CHAC1 upregulation. Clinically, tumor CHAC1 correlates with clinical benefits and improved survival in cancer patients treated with checkpoint blockades. Lastly, the triple combination of methionine intermittent deprivation, system xc- inhibitor and PD-1 blockade shows superior antitumor efficacy. Thus, intermittent methionine deprivation is a promising regimen to target ferroptosis and augment cancer immunotherapy.

Adenylyl-Sulfate Kinase (Met14)-Dependent Cysteine and Methionine Biosynthesis Pathways Contribute Distinctively to Pathobiological Processes in Cryptococcus neoformans

Blocking of nutrient uptake and amino acid biosynthesis are considered potential targets for next-generation antifungal drugs against pathogenic fungi, including Cryptococcus neoformans. In this regard, the sulfate assimilation pathway is particularly attractive, as it is only present in eukaryotes such as plants and fungi, yet not in mammals. Here, we demonstrated that the adenylyl sulfate kinase (Met14) in the sulfate assimilation pathway is not essential yet is required for the viability of C. neoformans due to its involvement in biosynthesis of two sulfur-containing amino acids, cysteine and methionine. Met14-dependent cysteine and methionine biosynthesis was found to significantly contribute to a diverse range of pathobiological processes in C. neoformans. Met14-dependent cysteine rather than methionine biosynthesis was also found to play pivotal roles in cell growth and tolerance to environmental stresses and antifungal drugs. In contrast, the Met14-dependent methionine biosynthesis was found to be more important than cysteine biosynthesis for the production of major cryptococcal virulence factors of melanin pigments and polysaccharide capsules. Finally, we also found that despite its attenuated virulence in an insect model, Galleria mellonella, the met14Δ mutant yielded no difference in virulence in a murine model of systemic cryptococcosis. Hence, clinical inhibition of Met14-dependent amino acid biosynthetic pathways may not be advantageous for the treatment of systemic cryptococcosis. IMPORTANCE Current antifungal drugs have several limitations, such as drug resistance, severe side effects, and a narrow spectrum. Therefore, novel antifungal targets are urgently needed. To this end, fungal sulfur amino acid biosynthetic pathways are considered potential targets for development of new antifungal agents. Here, we demonstrated that Met14 in the sulfate assimilation pathway promotes growth, stress response, and virulence factor production in C. neoformans via synthesis of sulfur-containing amino acids methionine and cysteine. Met14-dependent cysteine rather than methionine synthesis was found to be critical for growth and stress responses, whereas Met14-dependent methionine synthesis was more important for the production of antiphagocytic capsules and antioxidant melanin in C. neoformans. Surprisingly, deletion of the MET14 gene was found to attenuate cryptococcal virulence in an insect model, yet not in a murine model. Collectively, our results showed that Met14-dependent cysteine and methionine biosynthesis play roles that are distinct from each other in C. neoformans. Moreover, Met14 is unlikely to be a suitable anticryptococcal drug target.

Alkylcysteine Sulfoxide C-S Monooxygenase Uses a Flavin-Dependent Pummerer Rearrangement

Flavoenzymes are highly versatile and participate in the catalysis of a wide range of reactions, including key reactions in the metabolism of sulfur-containing compounds. S-Alkyl cysteine is formed primarily by the degradation of S-alkyl glutathione generated during electrophile detoxification. A recently discovered S-alkyl cysteine salvage pathway uses two flavoenzymes (CmoO and CmoJ) to dealkylate this metabolite in soil bacteria. CmoO catalyzes a stereospecific sulfoxidation, and CmoJ catalyzes the cleavage of one of the sulfoxide C-S bonds in a new reaction of unknown mechanism. In this paper, we investigate the mechanism of CmoJ. We provide experimental evidence that eliminates carbanion and radical intermediates and conclude that the reaction proceeds via an unprecedented enzyme-mediated modified Pummerer rearrangement. The elucidation of the mechanism of CmoJ adds a new motif to the flavoenzymology of sulfur-containing natural products and demonstrates a new strategy for the enzyme-catalyzed cleavage of C-S bonds.

Degradation of glutathione and glutathione conjugates in plants

Glutathione (GSH) is a ubiquitous, abundant, and indispensable thiol for plants that participates in various biological processes, such as scavenging reactive oxygen species, redox signaling, storage and transport of sulfur, detoxification of harmful substances, and metabolism of several compounds. Therefore knowledge of GSH metabolism is essential for plant science. Nevertheless, GSH degradation has been insufficiently elucidated, and this has hampered our understanding of plant life. Over the last five decades, the γ-glutamyl cycle has been dominant in GSH studies, and the exoenzyme γ-glutamyl transpeptidase has been regarded as the major GSH degradation enzyme. However, recent studies have shown that GSH is degraded in cells by cytosolic enzymes such as γ-glutamyl cyclotransferase or γ-glutamyl peptidase. Meanwhile, a portion of GSH is degraded after conjugation with other molecules, which has also been found to be carried out by vacuolar γ-glutamyl transpeptidase, γ-glutamyl peptidase, or phytochelatin synthase. These findings highlight the need to re-assess previous assumptions concerning the γ-glutamyl cycle, and a novel overview of the plant GSH degradation pathway is essential. This review aims to build a foundation for future studies by summarizing current understanding of GSH/glutathione conjugate degradation.

Critical Roles of the Cysteine-Glutathione Axis in the Production of γ-Glutamyl Peptides in the Nervous System

γ-Glutamyl moiety that is attached to the cysteine (Cys) residue in glutathione (GSH) protects it from peptidase-mediated degradation. The sulfhydryl group of the Cys residue represents most of the functions of GSH, which include electron donation to peroxidases, protection of reactive sulfhydryl in proteins via glutaredoxin, and glutathione conjugation of xenobiotics, whereas Cys-derived sulfur is also a pivotal component of some redox-responsive molecules. The amount of Cys that is available tends to restrict the capacity of GSH synthesis. In in vitro systems, cystine is the major form in the extracellular milieu, and a specific cystine transporter, xCT, is essential for survival in most lines of cells and in many primary cultivated cells as well. A reduction in the supply of Cys causes GPX4 to be inhibited due to insufficient GSH synthesis, which leads to iron-dependent necrotic cell death, ferroptosis. Cells generally cannot take up GSH without the removal of γ-glutamyl moiety by γ-glutamyl transferase (GGT) on the cell surface. Meanwhile, the Cys-GSH axis is essentially common to certain types of cells; primarily, neuronal cells that contain a unique metabolic system for intercellular communication concerning γ-glutamyl peptides. After a general description of metabolic processes concerning the Cys-GSH axis, we provide an overview and discuss the significance of GSH-related compounds in the nervous system.

Heat Stress-Induced Intestinal Barrier Impairment: Current Insights into the Aspects of Oxidative Stress and Endoplasmic Reticulum Stress

Heat stress (HS) occurs when the sensible temperature of animals exceeds their thermoregulatory capacity, a condition that exerts a detrimental impact on health and growth. The intestinal tract, as a highly sensitive organ, has been shown to respond to HS by exhibiting mucosal injury, intestinal leakage, and disturbances in the gut microbiota. Oxidative stress and endoplasmic reticulum stress (ERS) are both potential outcomes of long-term exposure to high temperatures and have been linked to apoptosis, autophagy, and ferroptosis. In addition, HS alters the composition of the gut microbiota accompanied by changed levels of bacterial components and metabolites, rendering the gut more vulnerable to stress-related injury. In this review, we present recent advances in mechanisms of oxidative stress-associated ERS in response to HS, which is destructive to intestinal barrier integrity. The involvement of autophagy and ferroptosis in ERS was highlighted. Further, we summarize the relevant findings regarding the engagement of gut microbiota-derived components and metabolites in modulation of intestinal mucosal injury induced by HS.

The ChaC1 active site: Defining the residues and determining the role of ChaC1-exclusive residues in the structural and functional stability

The glutathione degrading enzyme ChaC1 is highly upregulated in several cancers and viral infections making it a potential pharmacological target for cancer therapy. As an enzyme, however, ChaC1 has a relatively high K_m (~2 mM) towards its natural substrate, and therefore finding its inhibitors becomes very difficult. Given this limitation, a careful mapping of the active site has become necessary. In the current study, the enzyme-substrate complex was generated by docking glutathione with the modeled hChaC1 structure. Using a combination of in silico and wet lab approaches, the active site residues forming direct interactions with the substrate glutathione were identified and validated. Furthermore, the role of residues exclusively conserved in the ChaC family and forming the surface of the active site were also explored for their putative role in active site stabilization. Mutants of these residues have been analysed for their structural stability and interaction with the substrate through MD simulations and MMGBSA binding energy calculations. These findings were experimentally validated by assessment of their function through in vivo assays in yeast. The experimental evidences along with the molecular modeling suggest that residues 38'YGSL'41, D68, R72, E115, and Y143 are responsible for high affinity binding of hChaC1 with the substrate/inhibitor, whereas the residues exclusive to the ChaC family are required for the structural stability of the enzyme and its active site. Such a characterization of essential active site and conserved residues is significant as a key step toward rational design of novel inhibitors of the ChaC1 enzyme.

Glutathione system enhancement for cardiac protection: pharmacological options against oxidative stress and ferroptosis

The glutathione (GSH) system is considered to be one of the most powerful endogenous antioxidant systems in the cardiovascular system due to its key contribution to detoxifying xenobiotics and scavenging overreactive oxygen species (ROS). Numerous investigations have suggested that disruption of the GSH system is a critical element in the pathogenesis of myocardial injury. Meanwhile, a newly proposed type of cell death, ferroptosis, has been demonstrated to be closely related to the GSH system, which affects the process and outcome of myocardial injury. Moreover, in facing various pathological challenges, the mammalian heart, which possesses high levels of mitochondria and weak antioxidant capacity, is susceptible to oxidant production and oxidative damage. Therefore, targeted enhancement of the GSH system along with prevention of ferroptosis in the myocardium is a promising therapeutic strategy. In this review, we first systematically describe the physiological functions and anabolism of the GSH system, as well as its effects on cardiac injury. Then, we discuss the relationship between the GSH system and ferroptosis in myocardial injury. Moreover, a comprehensive summary of the activation strategies of the GSH system is presented, where we mainly identify several promising herbal monomers, which may provide valuable guidelines for the exploration of new therapeutic approaches.

The antioxidant glutathione

Reduced glutathione (GSH) is an essential non-enzymatic antioxidant in mammalian cells. GSH can act directly as an antioxidant to protect cells against free radicals and pro-oxidants, and as a cofactor for antioxidant and detoxification enzymes such as glutathione peroxidases, glutathione S-transferases, and glyoxalases. Glutathione peroxidases detoxify peroxides by a reaction that is coupled to GSH oxidation to glutathione disulfide (GSSG). GSSG is converted back to GSH by glutathione reductase and cofactor NADPH. GSH can regenerate vitamin E following detoxification reactions of vitamin E with lipid peroxyl radicals (LOO). GSH is a cofactor for GST during detoxification of electrophilic substances and xenobiotics. Dicarbonyl stress induced by methylglyoxal and glyoxal is alleviated by glyoxalase enzymes and GSH. GSH regulates redox signaling through reversible oxidation of critical protein cysteine residues by S-glutathionylation. GSH is involved in other cellular processes such as protein folding, protecting protein thiols from oxidation and crosslinking, degradation of proteins with disulfide bonds, cell cycle regulation and proliferation, ascorbate metabolism, apoptosis and ferroptosis.

Circadian Redox Rhythm in Plant-Fungal Pathogen Interactions

Significance: Circadian-controlled cellular growth, differentiation, and metabolism are mainly achieved by a classical transcriptional-translational feedback loop (TTFL), as revealed by investigations in animals, plants, and fungi. Recent Advances: Recently, reactive oxygen species (ROS) have been reported as part of a cellular network synchronizing nontranscriptional oscillators with established TTFL components, adding complexity to regulatory mechanisms of circadian rhythm. Both circadian rhythm and ROS homeostasis have a great impact on plant immunity as well as fungal pathogenicity, therefore interconnections of these two factors are implicit in plant-fungus interactions. Critical Issues: In this review, we aim to summarize the recent advances in circadian-controlled ROS homeostasis, or ROS-modulated circadian clock, in plant-fungus pathosystems, particularly using the rice (Oryza sativa) blast fungus (Magnaporthe oryzae) pathosystem as an example. Understanding of such bidirectional interaction between the circadian timekeeping machinery and ROS homeostasis/signaling would provide a theoretical basis for developing disease control strategies for important plants/crops. Future Directions: Questions remain unanswered about the detailed mechanisms underlying circadian regulation of redox homeostasis in M. oryzae, and the consequent fungal differentiation and death in a time-of-day manner. We believe that the rice-M. oryzae pathobiosystem would provide an excellent platform for investigating such issues in circadian-ROS interconnections in a plant-fungus interaction context. Antioxid. Redox Signal. 37, 726-738.

Hormesis and Oxidative Distress: Pathophysiology of Reactive Oxygen Species and the Open Question of Antioxidant Modulation and Supplementation

Alterations of redox homeostasis leads to a condition of resilience known as hormesis that is due to the activation of redox-sensitive pathways stimulating cell proliferation, growth, differentiation, and angiogenesis. Instead, supraphysiological production of reactive oxygen species (ROS) exceeds antioxidant defence and leads to oxidative distress. This condition induces damage to biomolecules and is responsible or co-responsible for the onset of several chronic pathologies. Thus, a dietary antioxidant supplementation has been proposed in order to prevent aging, cardiovascular and degenerative diseases as well as carcinogenesis. However, this approach has failed to demonstrate efficacy, often leading to harmful side effects, in particular in patients affected by cancer. In this latter case, an approach based on endogenous antioxidant depletion, leading to ROS overproduction, has shown an interesting potential for enhancing susceptibility of patients to anticancer therapies. Therefore, a deep investigation of molecular pathways involved in redox balance is crucial in order to identify new molecular targets useful for the development of more effective therapeutic approaches. The review herein provides an overview of the pathophysiological role of ROS and focuses the attention on positive and negative aspects of antioxidant modulation with the intent to find new insights for a successful clinical application.

Halotolerant Bacillus altitudinis WR10 improves salt tolerance in wheat via a multi-level mechanism

Soil salinity is an important abiotic stress factor that seriously affects the crop growth and yield. Use of plant-derived microorganisms is a promising strategy to alleviate salt stress. In a previous study, the endophytic strain Bacillus altitudinis WR10 isolated from wheat roots showed high salt resistance. In this study, we investigated the efficacy of WR10 in improving the salt tolerance of wheat and its potential mechanisms using a hydroponic test. Under salt stress, WR10 inoculation significantly increased the lengths and dry weights of the roots and shoots, indicating that WR10 improves wheat salt tolerance at the seedling stage. WR10 inoculation significantly reduced Na⁺ accumulation and enhanced K⁺, P, and Ca²⁺ uptake in salt-stressed plants, which can be attributed to the upregulated gene expression of H⁺-ATPase as well as the P-solubilizing and biofilm-producing characteristics of WR10. At the transcriptional level, L-ascorbate peroxidase (APX), glutathione (GSH) synthetase related to GSH biosynthesis, and phenylpropanoid biosynthesis genes (CYP73A, 4CL, and CAD) were significantly upregulated, whereas those of GSH metabolism genes (glutathione S-transferase and gamma-glutamyltranspeptidase) were significantly downregulated in WR10-applied wheat roots under salt stress. These changes increased the APX activity and GSH levels and resulted in a decrease in hydrogen peroxide levels. Additionally, a decrease in proline content was observed in WR10-inoculated plants under salt stress because of WR10-induced upregulation of proline dehydrogenase gene expression. These results provide supporting evidence that WR10 improves wheat salt tolerance via more than one mechanism and open a window of opportunity for WR10 application in salinized soil.

Genetic Disruption of the γ-Glutamylcysteine Ligase in PDAC Cells Induces Ferroptosis-Independent Cell Death In Vitro without Affecting In Vivo Tumor Growth

Simple Summary

The newly described form of iron-dependent cell death, called ferroptosis, has emerged as a powerful strategy for eradicating cancer cells. This is of particular importance for pancreatic ductal adenocarcinoma (PDAC), which has been shown to be one of the most aggressive tumors, with a five-year overall survival of less than 8%. The aim of the present study is to identify the most potent and selective target for the induction of ferroptosis in PDAC cells. The results presented here are of great importance not only for the development of novel and more effective anti-cancer therapeutics, but also anticipate potential resistant mechanisms that cancer cells might deploy. This way, ferroptosis-based therapeutics may be a step ahead of highly adaptable cancer cells.

Abstract

The conceptualization of a novel type of cell death, called ferroptosis, opens new avenues for the development of more efficient anti-cancer therapeutics. In this context, a full understanding of the ferroptotic pathways, the players involved, their precise role, and dispensability is prerequisite. Here, we focused on the importance of glutathione (GSH) for ferroptosis prevention in pancreatic ductal adenocarcinoma (PDAC) cells. We genetically deleted a unique, rate-limiting enzyme for GSH biosynthesis, γ-glutamylcysteine ligase (GCL), which plays a key role in tumor cell proliferation and survival. Surprisingly, although glutathione peroxidase 4 (GPx4) has been described as a guardian of ferroptosis, depletion of its substrate (GSH) led preferentially to apoptotic cell death, while classical ferroptotic markers (lipid hydroperoxides) have not been observed. Furthermore, the sensitivity of PDAC cells to the pharmacological/genetic inhibition of GPx4 revealed GSH dispensability in this context. To the best of our knowledge, this is the first time that the complete dissection of the xCT-GSH-GPx4 axis in PDAC cells has been investigated in great detail. Collectively, our results revealed the necessary role of GSH in the overall redox homeostasis of PDAC cells, as well as the dispensability of this redox-active molecule for a specific, antioxidant branch dedicated to ferroptosis prevention.

Naringin alleviates acetaminophen-induced acute liver injury by activating Nrf2 via CHAC2 upregulation

Severe acetaminophen (APAP)-induced hepatic damage is the second most common cause for hepatic transplantation. Clinically, hepatic damage caused by APAP is treated using N-acetyl-L-cysteine, which can induce numerous side effects. Naringin, a bioflavonoid abundant in grapefruit and other citrus fruits, displays marked antiinflammatory and antioxidant activities. Herein, we aimed to investigate the potential mechanism underlying naringin-mediated protection against APAP-induced acute hepatotoxicity. We observed that naringin afforded protection against APAP-induced acute liver failure in mice. Importantly, pretreatment with naringin before APAP administration further increased antioxidant enzyme expression, inhibited the production of proinflammatory cytokines, and activated apoptotic pathways. Furthermore, we observed that the protective effect was associated with the upregulation of cation transport regulator-like protein 2 (CHAC2) and nuclear factor erythroid derived-2-related factor 2 (Nrf2). Notably, CHAC2 knockdown inhibited Nrf2 activation and naringin-mediated antioxidant, antiinflammatory, and antiapoptotic effects in APAP-induced liver injury. Likewise, si-Nrf2 blocked the protective effect of naringin against APAP-induced liver injury. Collectively, our results indicate that naringin may be a potent CHAC2 activator, alleviating APAP-induced hepatitis via CHAC2-mediated activation of the Nrf2 pathway. These data provide new insights into mechanisms through which CHAC2 regulates APAP-induced liver injury by targeting Nrf2, which should be considered a novel therapeutic target.

Cysteine Dealkylation in Bacillus subtilis by a Novel Flavin-Dependent Monooxygenase

In this paper, we describe the biochemical reconstitution of a cysteine salvage pathway and the biochemical characterization of each of the five enzymes involved. The salvage begins with amine acetylation of S-alkylcysteine, followed by thioether oxidation. The C-S bond of the resulting sulfoxide is cleaved using a new flavoenzyme catalytic motif to give N-acetylcysteine sulfenic acid. This is then reduced to the thiol and deacetylated to complete the salvage pathway. We propose that this pathway is important in the catabolism of alkylated cysteine generated by proteolysis of alkylated glutathione formed in the detoxification of a wide range of electrophiles.

The Possible Mechanism of Physiological Adaptation to the Low-Se Diet and Its Health Risk in the Traditional Endemic Areas of Keshan Diseases

Selenium is an essential trace element for humans and animals. As with oxygen and sulfur, etc., it belongs to the sixth main group of the periodic table of elements. Therefore, the corresponding amino acids, such as selenocysteine (Sec), serine (Ser), and cysteine (Cys), have similar spatial structure, physical, and chemical properties. In this review, we focus on the neglected but key role of serine in a possible mechanism of the physiological adaptation to Se-deficiency in human beings with an adequate intake of dietary protein: the insertion of Cys in place of Sec during the translation of selenoproteins dependent on the Sec insertion sequence element in the 3'UTR of mRNA at the UGA codon through a novel serine-dependent pathway for the de novo synthesis of the Cys-tRNA^[Ser]Sec, similar to Sec-tRNA^[Ser]Sec. We also discuss the important roles of serine in the metabolism of selenium directly or indirectly via GSH, and the maintenance of selenium homostasis regulated through the methylation modification of Sec-tRNA^[Ser]Sec at the position 34U by SAM. Finally, we propose a hypothesis to explain why Keshan disease has gradually disappeared in China and predict the potential health risk of the human body in the physiological adaptation state of low selenium based on the results of animal experiments.

Probing the metabolism of γ-glutamyl peptides in cyanobacteria via metabolite profiling and 13 C labeling

Cyanobacteria are attractive model organisms for the study of photosynthesis and diurnal metabolism and as hosts for photoautotrophic production of chemicals. Exposure to bright light or environmental pollutants and a diurnal lifestyle of these prokaryotes may result in significant oxidative stress. Glutathione is a widely studied γ-glutamyl peptide that plays a key role in managing oxidative stress and detoxification of xenobiotics in cyanobacteria. The functional role and biosynthesis pathways of this tripeptide have been studied in detail in various phyla, including cyanobacteria. However, other γ-glutamyl peptides remain largely unexplored. We use an integrated approach to identify a number of γ-glutamyl peptides based on signature mass fragments and mass shifts in them in ¹³ C and ¹⁵ N enriched metabolite extracts. The newly identified compounds include γ-glutamyl dipeptides and derivatives of glutathione. Carbon backbones of the former turn over much faster than that of glutathione, suggesting that they follow a distinct biosynthesis pathway. Further, transients of isotopic ¹³ C enrichment show positional labeling in these peptides, which allows us to delineate the alternative biosynthesis pathways. Importantly, the amino acid of γ-glutamyl dipeptides shows much faster turnover compared to the glutamate moiety. The significant accumulation of γ-glutamyl dipeptides under slow-growth conditions combined with the results from dynamic ¹³ C labeling suggests that these compounds may act as reservoirs of amino acids in cyanobacteria.

Extracellular Enzyme Activities and Carbon/Nitrogen Utilization in Mycorrhizal Fungi Isolated From Epiphytic and Terrestrial Orchids

Fungi employ extracellular enzymes to initiate the degradation of organic macromolecules into smaller units and to acquire the nutrients for their growth. As such, these enzymes represent important functional components in terrestrial ecosystems. While it is well-known that the regulation and efficiency of extracellular enzymes to degrade organic macromolecules and nutrient-acquisition patterns strongly differ between major fungal groups, less is known about variation in enzymatic activity and carbon/nitrogen preference in mycorrhizal fungi. In this research, we investigated variation in extracellular enzyme activities and carbon/nitrogen preferences in orchid mycorrhizal fungi (OMF). Previous research has shown that the mycorrhizal fungi associating with terrestrial orchids often differ from those associating with epiphytic orchids, but whether extracellular enzyme activities and carbon/nitrogen preference differ between growth forms remains largely unknown. To fill this gap, we compared the activities of five extracellular enzymes [cellulase, xylanase, lignin peroxidase, laccase, and superoxide dismutase (SOD)] between fungi isolated from epiphytic and terrestrial orchids. In total, 24 fungal strains belonging to Tulasnellaceae were investigated. Cellulase and xylanase activities were significantly higher in fungi isolated from terrestrial orchids (0.050 ± 0.006 U/ml and 0.531 ± 0.071 U/ml, respectively) than those from epiphytic orchids (0.043 ± 0.003 U/ml and 0.295 ± 0.067 U/ml, respectively), while SOD activity was significantly higher in OMF from epiphytic orchids (5.663 ± 0.164 U/ml) than those from terrestrial orchids (3.780 ± 0.180 U/ml). Carboxymethyl cellulose was more efficiently used by fungi from terrestrial orchids, while starch and arginine were more suitable for fungi from epiphytic orchids. Overall, the results of this study show that extracellular enzyme activities and to a lesser extent carbon/nitrogen preferences differ between fungi isolated from terrestrial and epiphytic orchids and may indicate functional differentiation and ecological adaptation of OMF to local growth conditions.

Crosstalk between Endoplasmic Reticulum Stress and Oxidative Stress in Heat Exposure-Induced Apoptosis Is Dependent on the ATF4-CHOP-CHAC1 Signal Pathway in IPEC-J2 Cells

The intestinal epithelium is susceptible to heat stress (HS), which leads to gut leakage and inflammation. However, the mechanisms underlying HS-induced intestine dysfunction have yet to be elucidated. We established an in vitro chronic heat exposure-induced intestinal injury of intestinal porcine epithelial cells (IPEC-J2) exposed to high temperatures (43 °C) for 12 h. The results revealed that HS increased reactive oxygen species (ROS) generation and decreased superoxide dismutase 2 (SOD2) expression, leading to oxidative stress. Western blotting analysis demonstrated that HS induced apoptosis as evidenced by increased cytochrome c (Cyt c) release in the cytoplasm and caspase 3 activation. Transcriptome sequencing analysis revealed that HS activated the endoplasmic reticulum stress (ERS) response/unfolded protein response (UPR) but inhibited glutathione metabolism. Specifically, HS triggered the pro-apoptotic activating transcription factor 4 (ATF4)/CEBP-homologous protein (CHOP) branch of the UPR. Interestingly, glutathione-specific gamma-glutamylcyclotransferase1 (CHAC1) involved in glutathione degradation was upregulated due to heat exposure and was proved to be downstream of the ATF4-CHOP signal pathway. Knockdown of CHAC1 attenuated the HS-induced decrease in glutathione level and cell apoptosis. These studies suggest that crosstalk between ERS and oxidative stress in HS-induced apoptosis might be dependent on the ATF4-CHOP-CHAC1 signal pathway in IPEC-J2 cells.

Engineering the Redox-Driven Channel for Precisely Regulating Nanoconfined Glutathione Identification and Transport

Bioinspired artificial nanochannels for molecular and ionic transport have extensive applications. However, it is still a huge challenge to achieve an intelligent transport system with high selectivity/efficiency and controllability. Inspired by glutathione transport across the plasma membrane via redox regulation, we herein designed and fabricated a redox-reactive artificial nanochannel based on the host-guest chemical strategy. The nanochannel platform achieved high selectivity/efficiency for the identification and transmission of glutathione in the confined space. In addition, this nanochannel can switch between the ON and OFF states through the redox reaction. This redox-regulated system can provide a potential application for detection/binding of biological analytes and redox-controlled drug release.

Nano-Drug Design Based on the Physiological Properties of Glutathione

Glutathione (GSH) is involved in and regulates important physiological functions of the body as an essential antioxidant. GSH plays an important role in anti-oxidation, detoxification, anti-aging, enhancing immunity and anti-tumor activity. Herein, based on the physiological properties of GSH in different diseases, mainly including the strong reducibility of GSH, high GSH content in tumor cells, and the NADPH depletion when GSSH is reduced to GSH, we extensively report the design principles, effect, and potential problems of various nano-drugs in diabetes, cancer, nervous system diseases, fluorescent probes, imaging, and food. These studies make full use of the physiological and pathological value of GSH and develop excellent design methods of nano-drugs related to GSH, which shows important scientific significance and prominent application value for the related diseases research that GSH participates in or responds to.

Jejunal Transcriptomic Profiling for Differences in Feed Conversion Ratio in Slow-Growing Chickens

Simple Summary

The slow-growing Korat chicken (KR) is economically attractive, as KR meat has a high selling price and has thus been used in Thailand to support smallholder farmers. However, low feed efficiency in KR stockbreeding makes the product less competitive and improving KR feed efficiency is central to increasing KR profitability. Using RNA sequencing, we compared the jejunal transcriptomic profiles of low- and high-feed conversion ratio (FCR) KR chickens, to identify FCR-related transcriptional variation and biological pathways. Gene Ontology and Kyoto Encyclopedia of Gene and Genome analysis revealed that the main pathways involved in KR FCR variation are related to immune response, glutathione metabolism, vitamin transport and metabolism, lipid metabolism, and neuronal and cardiac maturation, development, and growth. This is the first study to investigate, in the jejunum, the molecular genetic mechanisms affecting the FCR of slow-growing chickens. These findings will be useful in line-breeding programs to improve feed efficiency and profitability in slow-growing chicken stockbreeding.

Abstract

Improving feed efficiency is an important breeding target for the poultry industry; to achieve this, it is necessary to understand the molecular basis of feed efficiency. We compared the jejunal transcriptomes of low- and high-feed conversion ratio (FCR) slow-growing Korat chickens (KRs). Using an original sample of 75 isolated 10-week-old KR males, we took jejunal samples from six individuals in two groups: those with extremely low FCR (n = 3; FCR = 1.93 ± 0.05) and those with extremely high FCR (n = 3; FCR = 3.29 ± 0.06). Jejunal transcriptome profiling via RNA sequencing revealed 56 genes that were differentially expressed (p < 0.01, FC > 2): 31 were upregulated, and 25 were downregulated, in the low-FCR group relative to the high-FCR group. Functional annotation revealed that these differentially expressed genes were enriched in biological processes related to immune response, glutathione metabolism, vitamin transport and metabolism, lipid metabolism, and neuronal and cardiac maturation, development, and growth, suggesting that these are important mechanisms governing jejunal feed conversion. These findings provide an important molecular basis for future breeding strategies to improve slow-growing chicken feed efficiency.

Ggct (γ-glutamyl cyclotransferase) plays an important role in erythrocyte antioxidant defense and red blood cell survival

The expression of GGCT (γ-glutamyl cyclotransferase) is upregulated in various human cancers. γ-glutamyl cyclotransferase enzyme activity was originally purified from human red blood cells (RBCs), but the physiological function of GGCT in RBCs is still not clear. Here we reported that Ggct deletion in mice leads to splenomegaly and progressive anaemia phenotypes, due to elevated oxidative damage and the shortened life span of Ggct^-/- RBCs. Ggct^-/- RBCs have increased reactive oxygen species (ROS), and are more sensitive to H₂ O₂ -induced damage compared to control RBCs. Glutathione (GSH) and GSH synthesis precursor l-cysteine are decreased in Ggct^-/- RBCs. Our study suggests a critical function of Ggct in RBC redox balance and life span maintenance through regulating GSH metabolism.

A robust ferroptosis-related gene signature predicts overall survival in clear cell renal cell carcinoma

Aims: To investigate the prognostic values and potential mechanisms of ferroptosis-related genes in clear cell renal cell carcinoma. Methods: Univariate Cox, least absolute shrinkage and selection operator regression and multivariate Cox regression analyses were employed to identify prognosis-related hub ferroptosis-related genes and establish a prognostic model. Results: The authors established a novel clinical predictive model based on seven hub ferroptosis-related genes in The Cancer Genome Atlas training cohort (n = 374) that was verified in the testing cohort (n = 156) and the entire group (n = 530). Functional analysis indicated that several carcinogenic pathways were enriched. Tumor-infiltrating cells and immunosuppressive molecules were significantly different between the two risk groups. Conclusion: Collectively, the authors successfully constructed a novel ferroptosis-related risk signature that was significantly associated with the prognosis of clear cell renal cell carcinoma.

Transcriptome analysis of MBD5-associated neurodevelopmental disorder (MAND) neural progenitor cells reveals dysregulation of autism-associated genes

MBD5-associated neurodevelopmental disorder (MAND) is an autism spectrum disorder (ASD) characterized by intellectual disability, motor delay, speech impairment and behavioral problems; however, the biological role of methyl-CpG-binding domain 5, MBD5, in neurodevelopment and ASD remains largely undefined. Hence, we created neural progenitor cells (NPC) derived from individuals with chromosome 2q23.1 deletion and conducted RNA-seq to identify differentially expressed genes (DEGs) and the biological processes and pathways altered in MAND. Primary skin fibroblasts from three unrelated individuals with MAND and four unrelated controls were converted into induced pluripotent stem cell (iPSC) lines, followed by directed differentiation of iPSC to NPC. Transcriptome analysis of MAND NPC revealed 468 DEGs (q < 0.05), including 20 ASD-associated genes. Comparison of DEGs in MAND with SFARI syndromic autism genes revealed a striking significant overlap in biological processes commonly altered in neurodevelopmental phenotypes, with TGFβ, Hippo signaling, DNA replication, and cell cycle among the top enriched pathways. Overall, these transcriptome deviations provide potential connections to the overlapping neurocognitive and neuropsychiatric phenotypes associated with key high-risk ASD genes, including chromatin modifiers and epigenetic modulators, that play significant roles in these disease states.

Non-linear relationship between gamma-glutamyl transferase and type 2 diabetes mellitus risk: secondary analysis of a prospective cohort study

OBJECTIVE

To investigate the association between gamma-glutamyl transferase (GGT) and type 2 diabetes mellitus (T2DM) risk.

METHODS

This was a secondary analysis based on a publicly available DRYAD dataset that included 15 444 study participants that received medical examinations at a single centre in Japan between 2004 and 2015. Crude, minimally-adjusted and fully-adjusted regression models were used to evaluate the relationship between GGT levels and T2DM risk.

RESULTS

The study participants (mean ± SD age of 43.72 ± 8.90 years; 8415 of 15 444 [54.49%] were male) were followed-up for a median of 1968 days (5.39 years). After adjusting for potential covariates, a non-linear relationship between the baseline GGT level and T2DM incidence was observed. The inflection point for T2DM risk was 10 IU/l GGT; below this point, the T2DM incidence increased by 1.18-fold per unit change in GGT. Above this point, the association between GGT and the incidence rate of T2DM became nonsignificant.

CONCLUSION

Baseline GGT exhibited a non-linear association with T2DM incidence. Elevated GGT levels should be incorporated into routine screening for individuals at high risk of T2DM, allowing for early intervention targeting GGT to potentially reduce T2DM-related morbidity.

Heart failure and the glutathione cycle: an integrated view

Heart failure results from the heart's inability to carryout ventricular contraction and relaxation, and has now become a worldwide problem. During the onset of heart failure, several signatures are observed in cardiomyocytes that includes fetal reprogramming of gene expression where adult genes are repressed and fetal genes turned on, endoplasmic reticulum stress and oxidative stress. In this short review and analysis, we examine these different phenomenon from the viewpoint of the glutathione cycle and the role of the recently discovered Chac1 enzyme. Chac1, which belongs to the family of γ-glutamylcyclotransferases, is a recently discovered member of the glutathione cycle, being involved in the cytosolic degradation of glutathione. This enzyme is induced during the Endoplasmic Stress response, but also in the developing heart. Owing to its exclusive action on reduced glutathione, its induction leads to an increase in the oxidative redox potential of the cell that also serves as signaling mechanism for calcium ions channel activation. The end product of Chac1 action is 5-oxoproline, and studies with 5-oxoprolinase (OPLAH), an enzyme of the glutathione cycle has revealed that down-regulation of OPLAH can lead to the accumulation of 5-oxproline which is an important factor in heart failure. With these recent findings, we have re-examined the roles and regulation of the enzymes in the glutathione cycle which are central to these responses. We present an integrated view of the glutathione cycle in the cellular response to heart failure.

Activation of NRF2 and ATF4 Signaling by the Pro-Glutathione Molecule I-152, a Co-Drug of N-Acetyl-Cysteine and Cysteamine

I-152 combines two pro-glutathione (GSH) molecules, namely N-acetyl-cysteine (NAC) and cysteamine (MEA), to improve their potency. The co-drug efficiently increases/replenishes GSH levels in vitro and in vivo; little is known about its mechanism of action. Here we demonstrate that I-152 not only supplies GSH precursors, but also activates the antioxidant kelch-like ECH-associated protein 1/nuclear factor E2-related factor 2 (KEAP1/NRF2) pathway. The mechanism involves disulfide bond formation between KEAP1 cysteine residues, NRF2 stabilization and enhanced expression of the γ-glutamil cysteine ligase regulatory subunit. Accordingly, a significant increase in GSH levels, not reproduced by treatment with NAC or MEA alone, was found. Compared to its parent compounds, I-152 delivered NAC more efficiently within cells and displayed increased reactivity to KEAP1 compared to MEA. While at all the concentrations tested, I-152 activated the NRF2 pathway; high doses caused co-activation of activating transcription factor 4 (ATF4) and ATF4-dependent gene expression through a mechanism involving Atf4 transcriptional activation rather than preferential mRNA translation. In this case, GSH levels tended to decrease over time, and a reduction in cell proliferation/survival was observed, highlighting that there is a concentration threshold which determines the transition from advantageous to adverse effects. This body of evidence provides a molecular framework for the pro-GSH activity and dose-dependent effects of I-152 and shows how synergism and cross reactivity between different thiol species could be exploited to develop more potent drugs.

The impact of glutathione metabolism in autism spectrum disorder

This paper reviews the potential role of glutathione (GSH) in autism spectrum disorder (ASD). GSH plays a key role in the detoxification of xenobiotics and maintenance of balance in intracellular redox pathways. Recent data showed that imbalances in the GSH redox system are an important factor in the pathophysiology of ASD. Furthermore, ASD is accompanied by decreased concentrations of reduced GSH in part caused by oxidation of GSH into glutathione disulfide (GSSG). GSSG can react with protein sulfhydryl (SH) groups, thereby causing proteotoxic stress and other abnormalities in SH-containing enzymes in the brain and blood. Moreover, alterations in the GSH metabolism via its effects on redox-independent mechanisms are other processes associated with the pathophysiology of ASD. GSH-related regulation of glutamate receptors such as the N-methyl-D-aspartate receptor can contribute to glutamate excitotoxicity. Synergistic and antagonistic interactions between glutamate and GSH can result in neuronal dysfunction. These interactions can involve transcription factors of the immune pathway, such as activator protein 1 and nuclear factor (NF)-κB, thereby interacting with neuroinflammatory mechanisms, ultimately leading to neuronal damage. Neuronal apoptosis and mitochondrial dysfunction are recently outlined as significant factors linking GSH impairments with the pathophysiology of ASD. Moreover, GSH regulates the methylation of DNA and modulates epigenetics. Existing data support a protective role of the GSH system in ASD development. Future research should focus on the effects of GSH redox signaling in ASD and should explore new therapeutic approaches by targeting the GSH system.

Dietary γ-Glutamylcysteine: Its Impact on Glutathione Status and Potential Health Outcomes

Glutathione (GSH) is a tripeptide that is readily synthesized intracellularly in humans and other mammals. More than a century of research suggests that GSH has numerous biological functions, including protection from the potential adverse events associated with reactive oxygen species (ROS) and related redox reactions that may induce oxidative stress, and that may be linked to innate detoxification processes. Normal tissue and plasma levels of GSH decline through the aging process and decrease during various disease states. While the health value of dietary GSH remains controversial, there is evidence that some metabolic intermediates, such as γ-glutamylcysteine (GGC) may function to preserve adequate GSH levels when the synthetic pathways decline in activity, and the innate antioxidant system is challenged. It is also important to recognize that among the thousands of protein-coding human genes and their respective polymorphisms, at least two genes (Gclc and Gclm) are directly involved with GSH synthesis via glutamate-cysteine ligase. This commentary examines the classic biochemistry, toxicology, safety, and clinical value of GSH and its intermediates that may be modulated by dietary supplementation.

The dark side of gamma-glutamyltransferase (GGT): Pathogenic effects of an 'antioxidant' enzyme

Having long been regarded as just a member in the cellular antioxidant systems, as well as a clinical biomarker of hepatobiliary diseases and alcohol abuse, gamma-glutamyltransferase (GGT) enzyme activity has been highlighted by more recent research as a critical factor in modulation of redox equilibria within the cell and in its surroundings. Moreover, due to the prooxidant reactions which can originate during its metabolic function in selected conditions, experimental and clinical studies are increasingly involving GGT in the pathogenesis of several important disease conditions, such as atherosclerosis, cardiovascular diseases, cancer, lung inflammation, neuroinflammation and bone disorders. The present article is an overview of the laboratory findings that have prompted an evolution in interpretation of the significance of GGT in human pathophysiology.

The glutathione system in Parkinson's disease and its progression

Redox dysfunctions and neuro-oxidative stress play a major role in the pathophysiology and progression of Parkinson's disease (PD). Glutathione (GSH) and the reduced/oxidized glutathione (GSH/GSSG) ratio are lowered in oxidative stress conditions and may lead to increased oxidative toxicity. GSH is involved not only in neuro-immune and neuro-oxidative processes, including thiol redox signaling, but also in cell proliferation and differentiation and in the regulation of cell death, including apoptotic pathways. Lowered GSH metabolism and a low GSH/GSSG ratio following oxidative stress are associated with mitochondrial dysfunctions and constitute a critical factor in the neuroinflammatory and neurodegenerative processes accompanying PD. This review provides indirect evidence that GSH redox signaling is associated with the pathophysiology of PD. Nevertheless, it has not been delineated whether GSH redox imbalances are a causative factor in PD or whether PD-associated pathways cause the GSH redox imbalances in PD. The results show that antioxidant approaches, including neuroprotective and anti-neuroinflammatory agents, which neutralize reactive oxygen species, may have therapeutic efficacy in the treatment of PD and its progression.

Chemistry and Biochemistry of Sulfur Natural Compounds: Key Intermediates of Metabolism and Redox Biology

Sulfur contributes significantly to nature chemical diversity and thanks to its particular features allows fundamental biological reactions that no other element allows. Sulfur natural compounds are utilized by all living beings and depending on the function are distributed in the different kingdoms. It is no coincidence that marine organisms are one of the most important sources of sulfur natural products since most of the inorganic sulfur is metabolized in ocean environments where this element is abundant. Terrestrial organisms such as plants and microorganisms are also able to incorporate sulfur in organic molecules to produce primary metabolites (e.g., methionine, cysteine) and more complex unique chemical structures with diverse biological roles. Animals are not able to fix inorganic sulfur into biomolecules and are completely dependent on preformed organic sulfurous compounds to satisfy their sulfur needs. However, some higher species such as humans are able to build new sulfur-containing chemical entities starting especially from plants' organosulfur precursors. Sulfur metabolism in humans is very complicated and plays a central role in redox biochemistry. The chemical properties, the large number of oxidation states, and the versatile reactivity of the oxygen family chalcogens make sulfur ideal for redox biological reactions and electron transfer processes. This review will explore sulfur metabolism related to redox biochemistry and will describe the various classes of sulfur-containing compounds spread all over the natural kingdoms. We will describe the chemistry and the biochemistry of well-known metabolites and also of the unknown and poorly studied sulfur natural products which are still in search for a biological role.

Transcriptomic analysis of the effect of (E)-3-(3,5-dimethoxyphenyl)-1-(2-methoxyphenyl) prop-2-en-1-one (DPP23) on reactive oxygen species generation in MIA PaCa-2 pancreatic cancer cells

BACKGROUND

Reactive oxygen species (ROS) generation specifically in cancer cells may be a promising strategy for their selective killing. The synthetic chalcone derivative (E)-3-(3,5-dimethoxyphenyl)-1-(2-methoxyphenyl)prop-2-en-1-one (DPP23) exerts antitumor activity through ROS-mediated apoptosis in cancer cells but not in healthy cells. However, the mechanism underlying ROS generation by DPP23 remains unknown.

OBJECTIVE

The current study aims to identify possible DPP23 target genes responsible for ROS generation through the mining of microarray data stored in NCBI's Gene Expression Omnibus (GEO).

METHODS

A comprehensive expression profile of genes modulated by DPP23 was examined by gene ontology analysis. DPP23-modulated genes in Mia-PaCa2 pancreatic cells were validated by reverse transcription-PCR.

RESULTS

Multiple genes were up and downregulated by DPP23 treatment in MiaPaCa2 pancreatic cancer cells. Genes with absolute fold-change (FC) of > 2 were selected as the cut-off criteria and grouped into 10 clusters to analyze expression patterns systematically. We observed that genes with increased expression at 6 h were significantly affected by ROS increase, unfolded protein response, and cell death. Expression of 13 genes involved in glutathione metabolism, including CHAC1, GCLC, G6PD, GSTO2, GSTA5, GSTM2, GSR, GPX3/6/8, GGT1, PGD, ATF4, and NAT8B, are modulated by DPP23. Of these, CHAC1 was most highly upregulated upon DPP23 treatment.

CONCLUSION

DPP23 alters global gene expression associated with multiple cellular responses, including oxidative stress and apoptosis. We found that DPP23 may induce GSH depletion through modulation of gene expression, which is especially involved in glutathione metabolism. Of these, CHAC1 emerged as the most prominent candidate for DPP23 as it was the most responsive to DPP23 treatment.

Metabolomic analysis of spontaneous neutrophil apoptosis reveals the potential involvement of glutathione depletion

Spontaneous apoptosis of neutrophils plays a key role in maintaining immune homeostasis and resolving inflammation. However, the mechanism triggering this apoptosis remains obscure. In the present study, we performed a global metabolomics analysis of neutrophils undergoing spontaneous apoptosis by using hydrophilic interaction chromatography ultra-high-performance liquid chromatography-tandem quadrupole/time-of-flight mass spectrometry and found 23 metabolites and 42 related pathways that were altered in these cells. Among them, glutathione, which is known to be involved in apoptosis, was particularly interesting. We found that L-pyroglutamic acid, glutamate, and their glutathione-mediated embolic pathways were all changed. Our findings confirmed the glutathione levels decreased in apoptotic neutrophils. Exogenous glutathione and LPS treatment delayed neutrophil apoptosis and decreased the levels of pro-apoptotic protein caspase-3. γ-glutamylcyclotransferase, 5-oxoprolinase, and ChaC1, which participated in glutathione degradation, were all activated. At the same time, the down-regulation of ATP production suggested the activity of glutathione biosynthesis may be attenuated even if glutamate-cysteine ligase and glutathione synthase, which are two ATP-dependent enzymes participating in glutathione biosynthesis, were enhanced. To our knowledge, this is the first report highlighting a global metabolomics analysis using hydrophilic interaction chromatography ultra-high-performance liquid chromatography-tandem quadrupole/time-of-flight mass spectrometry and the potential involvement of glutathione depletion in spontaneous apoptosis of neutrophils demonstrating that LPS could delay this process.

Cigarette smoke and glutathione: Focus on in vitro cell models

Cigarette smoke (CS) is one of the most important preventable risk factors for the development of respiratory diseases, cardiovascular diseases, stroke, and various types of cancer. Due to its high intracellular concentration and central role in maintaining the cellular redox state, glutathione (GSH) is one of the key players in several enzymatic and non-enzymatic reactions necessary for protecting cells against CS-induced oxidative stress. A plethora of in vitro cell models have been used over the years to assess the effects of CS on intracellular GSH and its disulphide forms, i.e. glutathione disulphide (GSSG) and S-glutathionylated proteins. In this review, we described the effects of cell exposure to CS on cellular GSH and formation of its oxidized forms and adducts (GSH-conjugates). We also discussed the limitations and relevance of in vitro cell models of exposure to CS and critically assessed the congruence between smokers and in vitro cell models. What emerges clearly is that results obtained in vitro should be interpreted with extreme caution, bearing in mind the limitations of the specific cell model used. Despite this, in vitro cell models remain important tools in the assessment of CS-induced oxidative damage.

The role of cysteine and sulfide in the interplay between microbial Hg(ii) uptake and sulfur metabolism

Biogenic thiols, such as cysteine, have been used to control the speciation of Hg(ii) in bacterial exposure experiments. However, the extracellular biodegradation of excess cysteine leads to the formation of Hg(ii)-sulfide species, convoluting the interpretation of Hg(ii) uptake results. Herein, we test the hypothesis that Hg(ii)-sulfide species formation is a critical step during bacterial Hg(ii) uptake in the presence of excess cysteine. An Escherichia coli (E. coli) wild-type and mutant strain lacking the decR gene that regulates cysteine degradation to sulfide were exposed to 50 and 500 nM Hg with 0 to 2 mM cysteine. The decR mutant released ∼4 times less sulfide from cysteine degradation compared to the wild-type for all tested cysteine concentrations during a 3 hour exposure period. We show with thermodynamic calculations that the predicted concentration of Hg(ii)-cysteine species remaining in the exposure medium (as opposed to forming HgS(s)) is a good proxy for the measured concentration of dissolved Hg(ii) (i.e., not cell-bound). Likewise, the measured cell-bound Hg(ii) correlates with thermodynamic calculations for HgS(s) formation in the presence of cysteine. High resolution X-ray absorption near edge structure (HR-XANES) spectra confirm the existence of cell-associated HgS(s) at 500 nM total Hg and suggest the formation of Hg-S clusters at 50 nM total Hg. Our results indicate that a speciation change to Hg(ii)-sulfide controls Hg(ii) cell-association in the presence of excess cysteine.