Reductive stress linked to small HSPs, G6PD, and Nrf2 pathways in heart disease

Redox remodeling of central metabolism as a driving force for cellular protection, proliferation, differentiation, and dysfunction

The production of reactive oxygen species (ROS) is elevated via metabolic hyperactivation in response to a variety of stimuli such as growth factors and inflammation. Tolerable amounts of ROS moderately inactivate enzymes via oxidative modification, which can be reversed back to the native form in a redox-dependent manner. The excessive production of ROS, however, causes cell dysfunction and death. Redox-reactive enzymes are present in primary metabolic pathways such as glycolysis and the tricarboxylic acid cycle, and these act as floodgates for carbon flux. Oxidation of a specific form of cysteine inhibits glyceraldehyde-3-phosphate dehydrogenase, which is reversible, and causes an accumulation of upstream intermediary compounds that increases the flux of glucose-6-phosphate to the pentose phosphate pathway. These reactions increase the NADPH and ribose-5-phosphate that are available for reductive reactions and nucleotide synthesis, respectively. On the other hand, oxidative inactivation of mitochondrial aconitase increases citrate, which is then recruited to synthesize fatty acids in the cytoplasm. Decreases in the use of carbohydrate for ATP production can be compensated via amino acid catabolism, and this metabolic change makes nitrogen available for nucleic acid synthesis. Coupling of the urea cycle also converts nitrogen to urea and polyamine, the latter of which supports cell growth. This metabolic remodeling stimulates the proliferation of tumor cells and fibrosis in oxidatively damaged tissues. Oxidative modification of these enzymes is generally reversible in the early stages of oxidizing reactions, which suggests that early treatment with appropriate antioxidants promotes the maintenance of natural metabolism.

Rosuvastatin ameliorates chemically induced acute lung injury in rats by targeting ferroptosis, heat shock protein B1, and inflammation

Acute lung injury (ALI) is a life-threatening condition characterized by respiratory failure. Rosuvastatin (RSV) is an antihypercholesterolemic agent with antioxidant properties. The current study aimed to investigate RSV novel therapeutic impact on ALI with emphasis on oxidative stress, inflammation, and heat shock protein B1 (HSPB1). Male albino rats (N = 30) were divided into five groups. Normal control (NC) group: rats received normal saline 2 mL/kg P.O daily. Lipopolysaccharides (LPS) group: rats received LPS (3 mg/kg intraperitoneally once). RSV group: rats received RSV (2 mg/kg P.O daily). LPS + RSV group: rats received RSV as in group 3 and on the 7th day rats received LPS as group 2. LPS + Dexamethasone (DX): rats received DX (2 mg/kg P.O, daily for one week) and on the 7th day rats received LPS as group 2. At the end of experiment (one week), lung tissue was used to determine HSPB1, high mobility group box 1 (HMGB1) using ELISA. IL-6, nuclear factor-2 (Nrf2), haem Oxygenase-1 (HO-1) protein levels were assessed using immunohistochemistry. GSH, catalase, MDA, NO, albumin and urea are assessed by colorimetry. The results revealed that RSV treatment resolved histopathological changes in lung tissue induced by LPS. Compared to LPS group, LPS + RSV group showed significant decrease in urea, NO, MDA, HMGB1, IL-6 and HO-1 level compared to LPS-treated rats. Conversely, RSV treatment significantly increased HSPB1, Nrf2, albumin, GSH, and CAT levels compared to LPS rats. RSV is effective for amelioration of ALI and thus can be used as adjuvant therapy for ALI.

Oxidative Metabolism as a Cause of Lipid Peroxidation in the Execution of Ferroptosis

Ferroptosis is a type of nonapoptotic cell death that is characteristically caused by phospholipid peroxidation promoted by radical reactions involving iron. Researchers have identified many of the protein factors that are encoded by genes that promote ferroptosis. Glutathione peroxidase 4 (GPX4) is a key enzyme that protects phospholipids from peroxidation and suppresses ferroptosis in a glutathione-dependent manner. Thus, the dysregulation of genes involved in cysteine and/or glutathione metabolism is closely associated with ferroptosis. From the perspective of cell dynamics, actively proliferating cells are more prone to ferroptosis than quiescent cells, which suggests that radical species generated during oxygen-involved metabolism are responsible for lipid peroxidation. Herein, we discuss the initial events involved in ferroptosis that dominantly occur in the process of energy metabolism, in association with cysteine deficiency. Accordingly, dysregulation of the tricarboxylic acid cycle coupled with the respiratory chain in mitochondria are the main subjects here, and this suggests that mitochondria are the likely source of both radical electrons and free iron. Since not only carbohydrates, but also amino acids, especially glutamate, are major substrates for central metabolism, dealing with nitrogen derived from amino groups also contributes to lipid peroxidation and is a subject of this discussion.

A big picture of the mitochondria-mediated signals: From mitochondria to organism

Mitochondria, well-known for years as the powerhouse and biosynthetic center of the cell, are dynamic signaling organelles beyond their energy production and biosynthesis functions. The metabolic functions of mitochondria, playing an important role in various biological events both in physiological and stress conditions, transform them into important cellular stress sensors. Mitochondria constantly communicate with the rest of the cell and even from other cells to the organism, transmitting stress signals including oxidative and reductive stress or adaptive signals such as mitohormesis. Mitochondrial signal transduction has a vital function in regulating integrity of human genome, organelles, cells, and ultimately organism.

Glucose-6-phosphate dehydrogenase deficiency and long-term risk of immune-related disorders

Introduction

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked enzymatic disorder that is particularly prevalent in Africa, Asia, and the Middle East. This study aimed to assess the long-term health risks associated with G6PD deficiency.

Methods

A retrospective cohort study was conducted using data from a national healthcare provider in Israel (Leumit Health Services). A total of 7,473 G6PD-deficient individuals were matched with 29,892 control subjects in a 1:4 ratio, based on age, gender, socioeconomic status, and ethnic groups. The exposure of interest was recorded G6PD diagnosis or positive G6PD diagnostic test. The main outcomes and measures included rates of infectious diseases, allergic conditions, and autoimmune disorders between 2002 and 2022.

Results

Significantly increased rates were observed for autoimmune disorders, infectious diseases, and allergic conditions in G6PD-deficient individuals compared to the control group. Specifically, notable increases were observed for rheumatoid arthritis (odds ratio [OR] 2.41, p<0.001), systemic lupus erythematosus (OR 4.56, p<0.001), scleroderma (OR 6.87, p<0.001), pernicious anemia (OR 18.70, p<0.001), fibromyalgia (OR 1.98, p<0.001), Graves' disease (OR 1.46, p=0.001), and Hashimoto's thyroiditis (OR 1.26, p=0.001). These findings were supported by elevated rates of positive autoimmune serology and higher utilization of medications commonly used to treat autoimmune conditions in the G6PD-deficient group.

Discussion

In conclusion, individuals with G6PD deficiency are at a higher risk of developing autoimmune disorders, infectious diseases, and allergic conditions. This large-scale observational study provides valuable insights into the comprehensive association between G6PD deficiency and infectious and immune-related diseases. The findings emphasize the importance of considering G6PD deficiency as a potential risk factor in clinical practice and further research is warranted to better understand the underlying mechanisms of these associations.

Carvedilol Phenocopies PGC-1α Overexpression to Alleviate Oxidative Stress, Mitochondrial Dysfunction and Prevent Doxorubicin-Induced Toxicity in Human iPSC-Derived Cardiomyocytes

Doxorubicin (DOX), one of the most effective and widely used anticancer drugs, has the major limitation of cancer treatment-related cardiotoxicity (CTRTOX) in the clinic. Reactive oxygen species (ROS) generation and mitochondrial dysfunction are well-known consequences of DOX-induced injury to cardiomyocytes. This study aimed to explore the mitochondrial functional consequences and associated mechanisms of pretreatment with carvedilol, a ß-blocking agent known to exert protection against DOX toxicity. When disease modeling was performed using cultured rat cardiac muscle cells (H9c2 cells) and human iPSC-derived cardiomyocytes (iPSC-CMs), we found that prophylactic carvedilol mitigated not only the DOX-induced suppression of mitochondrial function but that the mitochondrial functional readout of carvedilol-pretreated cells mimicked the readout of cells overexpressing the major regulator of mitochondrial biogenesis, PGC-1α. Carvedilol pretreatment reduces mitochondrial oxidants, decreases cell death in both H9c2 cells and human iPSC-CM and maintains the cellular 'redox poise' as determined by sustained expression of the redox sensor Keap1 and prevention of DOX-induced Nrf2 nuclear translocation. These results indicate that, in addition to the already known ROS-scavenging effects, carvedilol has a hitherto unrecognized pro-reducing property against the oxidizing conditions induced by DOX treatment, the sequalae of DOX-induced mitochondrial dysfunction and compromised cell viability. The novel findings of our preclinical studies suggest future trial design of carvedilol prophylaxis, such as prescreening for redox state, might be an alternative strategy for preventing oxidative stress writ large in lieu of the current lack of clinical evidence for ROS-scavenging agents.

A Flexible and Transparent PtNP/SWCNT/PET Electrochemical Sensor for Nonenzymatic Detection of Hydrogen Peroxide Released from Living Cells with Real-Time Monitoring Capability

We developed a transparent and flexible electrochemical sensor using a platform based on a network of single-walled carbon nanotubes (SWCNTs) for the non-enzymatic detection of hydrogen peroxide (H₂O₂) released from living cells. We decorated the SWCNT network on a poly(ethylene terephthalate) (PET) substrate with platinum nanoparticles (PtNPs) using a potentiodynamic method. The PtNP/SWCNT/PET sensor synergized the advantages of a flexible PET substrate, a conducting SWCNT network, and a catalytic PtNP and demonstrated good biocompatibility and flexibility, enabling cell adhesion. The PtNP/SWCNT/PET-based sensor demonstrated enhanced electrocatalytic activity towards H₂O₂, as well as excellent selectivity, stability, and reproducibility. The sensor exhibited a wide dynamic range of 500 nM to 1 M, with a low detection limit of 228 nM. Furthermore, the PtNP/SWCNT/PET sensor remained operationally stable, even after bending at various angles (15°, 30°, 60°, and 90°), with no noticeable loss of current signal. These outstanding characteristics enabled the PtNP/SWCNT/PET sensor to be practically applied for the direct culture of HeLa cells and the real-time monitoring of H₂O₂ release by the HeLa cells under drug stimulation.

The bridge between cell survival and cell death: reactive oxygen species-mediated cellular stress

As a requirement of aerobic metabolism, regulation of redox homeostasis is indispensable for the continuity of living homeostasis and life. Since the stability of the redox state is necessary for the maintenance of the biological functions of the cells, the balance between the pro-oxidants, especially ROS and the antioxidant capacity is kept in balance in the cells through antioxidant defense systems. The pleiotropic transcription factor, Nrf2, is the master regulator of the antioxidant defense system. Disruption of redox homeostasis leads to oxidative and reductive stress, bringing about multiple pathophysiological conditions. Oxidative stress characterized by high ROS levels causes oxidative damage to biomolecules and cell death, while reductive stress characterized by low ROS levels disrupt physiological cell functions. The fact that ROS, which were initially attributed as harmful products of aerobic metabolism, at the same time function as signal molecules at non-toxic levels and play a role in the adaptive response called mithormesis points out that ROS have a dose-dependent effect on cell fate determination. See also Figure 1(Fig. 1).

Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency and Long-Term Risk of Immune-Related diseases

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive enzymatic disorder, particularly prevalent in Africa, Asia and the Middle East. In the US, about 14% of black men are affected. Individuals with G6PD deficiency are often asymptomatic but may develop hemolysis following an infection or upon consumption of specific medications. Despite some evidence that G6PD deficiency affects the immune system, the long- term health risks associated with G6PD deficiency had not been studied in a large population.

METHODS

In this retrospective cohort study, health records from G6PD deficient individuals were compared to matched controls in a national healthcare provider in Israel (Leumit Health Services). Rates of infectious diseases, allergic conditions and autoimmune disorders were compared between groups.

RESULTS

The cohort included 7,473 G6PD deficient subjects (68.7% men) matched with 29,892 control subjects (4:1 ratio) of the same age, gender, socioeconomic status and ethnic group, followed during 14.3±6.2 years.Significantly increased rates for autoimmune disorders, infectious diseases and allergic conditions were observed throughout this period. Notable increases were observed for rheumatoid arthritis (OR 2.41, p<0.001), systemic lupus erythematosus (OR 4.56, p<0.001), scleroderma (OR 6.87, p<0.001), pernicious anemia (OR=18.70, P<0.001), fibromyalgia (OR 1.98, p<0.001), Graves' disease (OR 1.46, P=0.001), and Hashimoto's thyroiditis (OR 1.26, P=0.001). These findings were corroborated with elevated rates of positive autoimmune serology and higher rates of treatment with medications commonly used to treat autoimmune conditions in the G6PD deficient group.

CONCLUSION

G6PD deficient individuals suffer from higher rates of autoimmune disorders, infectious diseases, and allergic conditions.

The emergent role of mitochondrial surveillance in cellular health

Mitochondrial dysfunction is one of the primary causatives for many pathologies, including neurodegenerative diseases, cancer, metabolic disorders, and aging. Decline in mitochondrial functions leads to the loss of proteostasis, accumulation of ROS, and mitochondrial DNA damage, which further exacerbates mitochondrial deterioration in a vicious cycle. Surveillance mechanisms, in which mitochondrial functions are closely monitored for any sign of perturbations, exist to anticipate possible havoc within these multifunctional organelles with primitive origin. Various indicators of unhealthy mitochondria, including halted protein import, dissipated membrane potential, and increased loads of oxidative damage, are on the top of the lists for close monitoring. Recent research also indicates a possibility of reductive stress being monitored as part of a mitochondrial surveillance program. Upon detection of mitochondrial stress, multiple mitochondrial stress-responsive pathways are activated to promote the transcription of numerous nuclear genes to ameliorate mitochondrial damage and restore compromised cellular functions. Co-expression occurs through functionalization of transcription factors, allowing their binding to promoter elements to initiate transcription of target genes. This review provides a comprehensive summary of the intricacy of mitochondrial surveillance programs and highlights their roles in our cellular life. Ultimately, a better understanding of these surveillance mechanisms is expected to improve healthspan.

Transgenic Expression of Nrf2 Induces a Pro-Reductive Stress and Adaptive Cardiac Remodeling in the Mouse

Nuclear factor, erythroid 2 like 2 (Nfe2l2 or Nrf2), is a transcription factor that protects cells by maintaining a homeostatic redox state during stress. The constitutive expression of Nrf2 (CaNrf2-TG) was previously shown to be pathological to the heart over time. We tested a hypothesis that the cardiac-specific expression of full length Nrf2 (mNrf2-TG) would moderately increase the basal antioxidant defense, triggering a pro-reductive environment leading to adaptive cardiac remodeling. Transgenic and non-transgenic (NTG) mice at 7−8 months of age were used to analyze the myocardial transcriptome, structure, and function. Next generation sequencing (NGS) for RNA profiling and qPCR-based validation of the NGS data, myocardial redox levels, and imaging (echocardiography) were performed. Transcriptomic analysis revealed that out of 14,665 identified mRNAs, 680 were differently expressed (DEG) in TG hearts. Of 680 DEGs, 429 were upregulated and 251 were downregulated significantly (FC > 2.0, p < 0.05). Gene set enrichment analysis revealed that the top altered pathways were (a) Nrf2 signaling, (b) glutathione metabolism and (c) ROS scavenging. A comparative analysis of the glutathione redox state in the hearts demonstrated significant differences between pro-reductive vs. hyper-reductive conditions (233 ± 36.7 and 380 ± 68.7 vs. 139 ± 8.6 µM/mg protein in mNrf2-TG and CaNrf2-TG vs. NTG). Genes involved in fetal development, hypertrophy, cytoskeletal rearrangement, histone deacetylases (HDACs), and GATA transcription factors were moderately increased in mNrf2-TG compared to CaNrf2-TG. Non-invasive echocardiography analysis revealed an increase in systolic function (ejection fraction) in mNrf2-TG, suggesting an adaptation, as opposed to pathological remodeling in CaNrf2-TG mice experiencing a hyper-reductive stress, leading to reduced survival (40% at 60 weeks). The effects of excess Nrf2-driven antioxidant transcriptome revealed a pro-reductive condition in the myocardium leading to an adaptive cardiac remodeling. While pre-conditioning the myocardial redox with excess antioxidants (i.e., pro-reductive state) could be beneficial against oxidative stress, a chronic pro-reductive environment in the myocardium might transition the adaptation to pathological remodeling.

ATP-independent molecular chaperone activity generated under reducing conditions

Molecular chaperones are essential to maintain proteostasis. While the functions of intracellular molecular chaperones that oversee protein synthesis, folding and aggregation, are established, those specialized to work in the extracellular environment are less understood. Extracellular proteins reside in a considerably more oxidizing milieu than cytoplasmic proteins and are stabilized by abundant disulfide bonds. Hence, extracellular proteins are potentially destabilized and sensitive to aggregation under reducing conditions. We combine biochemical and mass spectrometry experiments and elucidate that the molecular chaperone functions of the extracellular protein domain Bri2 BRICHOS only appear under reducing conditions, through the assembly of monomers into large polydisperse oligomers by an intra- to intermolecular disulfide bond relay mechanism. Chaperone-active assemblies of the Bri2 BRICHOS domain are efficiently generated by physiological thiol-containing compounds and proteins, and appear in parallel with reduction-induced aggregation of extracellular proteins. Our results give insights into how potent chaperone activity can be generated from inactive precursors under conditions that are destabilizing to most extracellular proteins and thereby support protein stability/folding in the extracellular space. SIGNIFICANCE: Chaperones are essential to cells as they counteract toxic consequences of protein misfolding particularly under stress conditions. Our work describes a novel activation mechanism of an extracellular molecular chaperone domain, called Bri2 BRICHOS. This mechanism is based on reducing conditions that initiate small subunits to assemble into large oligomers via a disulfide relay mechanism. Activated Bri2 BRICHOS inhibits reduction-induced aggregation of extracellular proteins and could be a means to boost proteostasis in the extracellular environment upon reductive stress.

Nrf2 signaling in the oxidative stress response after spinal cord injury

Spinal cord injury (SCI) is a central nervous system trauma that can cause severe neurological impairment. A series of pathological and physiological changes after SCI (e.g., inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction) promotes further deterioration of the microenvironment at the site of injury, leading to aggravation of neurological function. The multifunctional transcription factor NF-E2 related factor 2 (Nrf2) has long been considered a key factor in antioxidant stress. Therefore, Nrf2 may be an ideal therapeutic target for SCI. A comprehensive understanding of the function and regulatory mechanism of Nrf2 in the pathophysiology of SCI will aid in the development of targeted therapeutic strategies for SCI. This review discusses the roles of Nrf2 in SCI, with the aim of aiding in further elucidation of SCI pathophysiology and in efforts to provide Nrf2-targeted strategies for the treatment of SCI.

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

ER reductive stress caused by Ero1α S-nitrosation accelerates senescence

Oxidative stress in aging has attracted much attention; however, the role of reductive stress in aging remains largely unknown. Here, we report that the endoplasmic reticulum (ER) undergoes reductive stress during replicative senescence, as shown by specific glutathione and H₂O₂ fluorescent probes. We constructed an ER-specific reductive stress cell model by ER-specific catalase overexpression and observed accelerated senescent phenotypes accompanied by disrupted proteostasis and a compromised ER unfolded protein response (UPR). Mechanistically, S-nitrosation of the pivotal ER sulfhydryl oxidase Ero1α led to decreased activity, therefore resulting in reductive stress in the ER. Inhibition of inducible nitric oxide synthase decreased the level of Ero1α S-nitrosation and decreased cellular senescence. Moreover, the expression of constitutively active Ero1α restored an oxidizing state in the ER and successfully rescued the senescent phenotypes. Our results uncover a new mechanism of senescence promoted by ER reductive stress and provide proof-of-concept that maintaining the oxidizing power of the ER and organelle-specific precision redox regulation could be valuable future geroprotective strategies.

Metformin inhibits the tumor-promoting effect of low-dose resveratrol, and enhances the anti-tumor activity of high-dose resveratrol by increasing its reducibility in triple negative breast cancer

Resveratrol, a natural antioxidant that maintains better bioactivity under hypoxia, has anti-tumor effects, but its underlying mechanism is controversial and the effect on Triple-negative breast cancer (TNBC) remains unclear. Herein, we investigated the anti-TNBC mechanism of resveratrol under a mimic hypoxic tumor microenvironment and explored a method of combining metformin to improve the therapeutic effect. The results showed an inverted "U" shaped relationship between the cell viability and resveratrol concentrations. Low concentrations of resveratrol (LRes) promoted proliferation and migration in MDA-MB-231 cells by activating JAK3/STAT3 signaling pathway, while high concentrations of resveratrol (HRes) inhibited cell growth and induced both autophagy and apoptosis through MAPK signaling pathway. Meanwhile, HRes treatment resulted in the up-regulation of antioxidant-related genes SOD3 and FAM213B, the increase of catalase activity and NAD(P)H level, which leading to a reducing microenvironment in cells. Notably, metformin could inhibit the proliferation and migration induced by LRes, whereas promote apoptosis induced by HRes. Moreover, metformin enhanced the reducing environment via further increasing the catalase activity and NAD(P)H level. These findings conclude the anti-TNBC mechanism of HRes should be attributed to its antioxidant activity and metformin enhances its reducibility. Metformin combined with resveratrol exerts a synergistic therapeutic effect on TNBC and effectively prevents tumor progression.

Antioxidant Paradox in Male Infertility: 'A Blind Eye' on Inflammation

The pathophysiology of male infertility involves various interlinked endogenous pathways. About 50% of the cases of infertility in men are idiopathic, and oxidative stress (OS) reportedly serves as a central mechanism in impairing male fertility parameters. The endogenous antioxidant system operates to conserve the seminal redox homeostasis required for normal male reproduction. OS strikes when a generation of seminal reactive oxygen species (ROS) overwhelms endogenous antioxidant capacity. Thus, antioxidant treatment finds remarkable relevance in the case of idiopathic male infertility or subfertility. However, due to lack of proper detection of OS in male infertility, use of antioxidant(s) in some cases may be arbitrary or lead to overuse and induction of 'reductive stress'. Moreover, inflammation is closely linked to OS and may establish a vicious loop that is capable of disruption to male reproductive tissues. The result is exaggeration of cellular damage and disruption of male reproductive tissues. Therefore, limitations of antioxidant therapy in treating male infertility are the failure in the selection of specific treatments targeting inflammation and OS simultaneously, two of the core mechanisms of male infertility. The present review aims to elucidate the antioxidant paradox in male infertility treatment, from the viewpoints of both induction of reductive stress as well as overlooking the inflammatory consequences.

Reductive Stress and Male Infertility

Male infertility research and clinical advances had vast progress in the last few decades. Strong research evidence underpinned the concepts of oxidative stress (OS)-mediated male reproductive disruptions, which bear answers to several cases of idiopathic male infertility. Antioxidant treatment held the prime solution for OS-mediated male infertility. But excess use of antioxidants is challenged by the research breakthrough that reductive stress also predisposes to male infertility, resolutely instituting that any biological extremes of the redox spectrum are deleterious to male fertility. Superfluity of reducing agents may hinder essential oxidation mechanisms, affecting physiological homeostasis. These mechanisms need to be explicated and updated time and again to identify the fine thread between OS-mediated male infertility treatment and induction of reductive stress. This chapter thus presents the evidence-based concepts pertaining to the antioxidants actions to combat OS-induced male infertility, the mechanism of induction of reductive stress and its impact on male reproduction.

The role of nuclear factor erythroid 2-related factor 2 (NRF2) in normal and pathological pregnancy: A systematic review

OBJECTIVE

A homeostatic balance between reactive oxygen species production and the antioxidant redox system is an important component of normal pregnancy. Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) preserves cellular homeostasis by enhancing the cell's innate antioxidant status to reduce oxidative stress and inflammatory damage to the cell during pregnancy. Active Nrf2, in the nucleus of the cell, transactivates various antioxidant genes. The objective of this systematic review was to synthesize evidence on the role of Nrf2 in various adverse pregnancy outcomes (APOs).

METHODS

We conducted a systematic review of the role of Nrf2 in pregnancy. Articles written in English, Portuguese, and Spanish were obtained from three different databases from inception until January 2021. The titles, abstracts and full text were reviewed independently by six reviewers. The quality of the included studies was assessed using a quality assessment tool developed to assess basic science and clinical studies. Nrf2 expression (gene and protein), functional contributions, and association with APOs were assessed.

RESULTS

A total of 747 citations were identified; 80 were retained for full review. Most studies on Nrf2 have been carried out using placental tissues and placenta-derived cells. Limited studies have been conducted using fetal membranes, uterus, and cervix. Nuclear translocation of Nrf2 results in transactivation of antioxidant enzymes, including glutathione peroxidase, hemeoxygenase-1, and superoxide dismutase in gestational cells during pregnancy. This antioxidant response maintains cellular homeostasis during pregnancy. This promotes trophoblast cell survival and prevents cell death and abnormal angiogenesis in the placenta. Excessive and insufficient Nrf2 response may promote oxidative and reductive stress, respectively. This Nrf2 dysregulation has been associated with APOs including gestational diabetes mellitus, intrauterine growth restriction, reproductive toxicity, preeclampsia, and preterm birth.

CONCLUSION

Several studies have localized and reported an association between Nrf2's differential expression in reproductive tissues and the pathogenesis of APOs. However, a comprehensive functional understanding of Nrf2 in reproductive tissues is still lacking. Nrf2's activation and functions are complex, and therefore, current in vitro and in vivo studies are limited in their experimental approaches. We have identified key areas for future Nrf2 research that is needed to fill knowledge gaps.

An NADH-selective and sensitive fluorescence probe to evaluate living cell hypoxic stress

Cellular disease and senescence are often accompanied by an imbalance in the local oxygen supply. Under hypoxia, mitochondrial NADH and FADH₂ cannot be oxidized by the mitochondrial electron transport chain, which leads to the accumulation of reducing equivalents and subsequent reduction stress. Detecting changes in intracellular NADH levels is expected to allow an assessment of stress. We synthesized a red fluorescent probe, DPMQL1, with high selectivity and sensitivity for detecting NADH in living cells. The probe DPMQL1 has strong anti-interference abilities toward various potential biological interferences, such as metal ions, anions, redox species, and other biomolecules. In addition, its detection limit can reach the nanomolar level, meaning it can display small changes in NADH levels in living cells, so as to realize the evaluation of cell-based hypoxic stress.

Identification of Nrf2-responsive microRNA networks as putative mediators of myocardial reductive stress

Although recent advances in the treatment of acute coronary heart disease have reduced mortality rates, few therapeutic strategies exist to mitigate the progressive loss of cardiac function that manifests as heart failure. Nuclear factor, erythroid 2 like 2 (Nfe2l2, Nrf2) is a transcriptional regulator that is known to confer transient myocardial cytoprotection following acute ischemic insult; however, its sustained activation paradoxically causes a reductive environment characterized by excessive antioxidant activity. We previously identified a subset of 16 microRNAs (miRNA) significantly diminished in Nrf2-ablated (Nrf2-/-) mouse hearts, leading to the hypothesis that increasing levels of Nrf2 activation augments miRNA induction and post-transcriptional dysregulation. Here, we report the identification of distinct miRNA signatures (i.e. "reductomiRs") associated with Nrf2 overexpression in a cardiac-specific and constitutively active Nrf2 transgenic (caNrf2-Tg) mice expressing low (TgL) and high (TgH) levels. We also found several Nrf2 dose-responsive miRNAs harboring proximal antioxidant response elements (AREs), implicating these "reductomiRs" as putative meditators of Nrf2-dependent post-transcriptional regulation. Analysis of mRNA-sequencing identified a complex network of miRNAs and effector mRNAs encoding known pathological hallmarks of cardiac stress-response. Altogether, these data support Nrf2 as a putative regulator of cardiac miRNA expression and provide novel candidates for future mechanistic investigation to understand the relationship between myocardial reductive stress and cardiac pathophysiology.

Regulation of Nrf2 signaling pathway in heart failure: Role of extracellular vesicles and non-coding RNAs

The balance between pro- and antioxidant molecules has been established as an important driving force in the pathogenesis of cardiovascular disease. Chronic heart failure is associated with oxidative stress in the myocardium and globally. Redox balance in the heart and brain is controlled, in part, by antioxidant proteins regulated by the transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2), which is reduced in the heart failure state. Nrf2 can, in turn, be regulated by a variety of mechanisms including circulating microRNAs (miRNAs) encapsulated in extracellular vesicles (EVs) derived from multiple cell types in the heart. Here, we review the role of the Nrf2 and antioxidant enzyme signaling pathway in mediating redox balance in the myocardium and the brain in the heart failure state. This review focuses on Nrf2 and antioxidant protein regulation in the heart and brain by miRNA-enriched EVs in the setting of heart failure. We discuss EV-mediated intra- and inter-organ communications especially, communication between the heart and brain via an EV pathway that mediates cardiac function and sympatho-excitation in heart failure. Importantly, we speculate how engineered EVs with specific miRNAs or antagomirs may be used in a therapeutic manner in heart failure.

Hydrogen selenide, a vital metabolite of sodium selenite, uncouples the sulfilimine bond and promotes the reversal of liver fibrosis

Sodium selenite has alleviating effects on liver fibrosis; however, its therapeutic molecular mechanism remains unclear. Herein, hydrogen selenide, a major metabolite of Na₂SeO₃, was tested to uncouple the sulfilimine bond in collagen IV, the biomarker of liver fibrosis. A mouse model of liver fibrosis was constructed via a CCl₄-induced method, followed by the administration of 0.2 mg kg^-1 Na₂SeO₃ via gavage three times per week for 4 weeks. Changes in H₂Se, NADPH, and H₂O₂ levels were monitored in real time by using NIR-H₂Se, DCI-MQ-NADPH, and H₂O₂ probes in vivo, respectively. H₂Se continuously accumulated in the liver throughout the Na₂SeO₃ treatment period, but the levels of NADPH and H₂O₂ decreased. The expression of collagen IV was analyzed through Western blot and liquid chromatography-mass spectrometry. Results confirmed that the sulfilimine bond of collagen IV in the fibrotic mouse livers could be broken by H₂Se with the Na₂SeO₃ treatment. Therefore, the therapeutic effect of Na₂SeO₃ on liver fibrosis could be mainly attributed to H₂Se that uncoupled the sulfilimine bond to induce collagen IV degradation. This study provided a reasonable explanation for the molecular mechanism of the in vivo function of Na₂SeO₃ and the prevention of liver fibrosis by administering inorganic selenium.

Sulfur Metabolism Under Stress

Significance: In humans, imbalances in the reduction-oxidation (redox) status of cells are associated with many pathological states. In addition, many therapeutics and prophylactics used as interventions for diverse pathologies either directly modulate oxidant levels or otherwise influence endogenous cellular redox systems. Recent Advances: The cellular machineries that maintain redox homeostasis or that function within antioxidant defense systems rely heavily on the regulated reactivities of sulfur atoms either within or derived from the amino acids cysteine and methionine. Recent advances have substantially advanced our understanding of the complex and essential chemistry of biological sulfur-containing molecules. Critical Issues: The redox machineries that maintain cellular homeostasis under diverse stresses can consume large amounts of energy to generate reducing power and/or large amounts of sulfur-containing nutrients to replenish or sustain intracellular stores. By understanding the metabolic pathways underlying these responses, one can better predict how to protect cells from specific stresses. Future Directions: Here, we summarize the current state of knowledge about the impacts of different stresses on cellular metabolism of sulfur-containing molecules. This analysis suggests that there remains more to be learned about how cells use sulfur chemistry to respond to stresses, which could in turn lead to advances in therapeutic interventions for some exposures or conditions.

Nuclear Factor Erythroid 2-Related Factor 2 in Regulating Cancer Metabolism

Significance: Nuclear factor erythroid 2 (NFE2)-related factor 2 (NFE2L2, or NRF2) is a transcription factor predominantly affecting the expression of antioxidant genes. NRF2 plays a significant role in the control of redox balance, which is crucial in cancer cells. NRF2 activation regulates numerous cancer hallmarks, including metabolism, cancer stem cell characteristics, tumor aggressiveness, invasion, and metastasis formation. We review the molecular characteristics of the NRF2 pathway and discuss its interactions with the cancer hallmarks previously listed. Recent Advances: The noncanonical activation of NRF2 was recently discovered, and members of this pathway are involved in carcinogenesis. Further, cancer-related changes (e.g., metabolic flexibility) that support cancer progression were found to be redox- and NRF2 dependent. Critical Issues: NRF2 undergoes Janus-faced behavior in cancers. The pro- or antineoplastic effects of NRF2 are context dependent and essentially based on the specific molecular characteristics of the cancer in question. Therefore, systematic investigation of NRF2 signaling is necessary to clarify its role in cancer etiology. The biggest challenge in the NRF2 field is to determine which cancers can be targeted for better clinical outcomes. Further, large-scale genomic and transcriptomic studies are missing to correlate the clinical outcome with the activity of the NRF2 system. Future Directions: To exploit NRF2 in a clinical setting in the future, the druggable members of the NRF2 pathway should be identified. In addition, it will be important to study how the modulation of the NRF2 system interferes with cytostatic drugs and their combinations.

Oxidative, Reductive, and Nitrosative Stress Effects on Epigenetics and on Posttranslational Modification of Enzymes in Cardiometabolic Diseases

Oxidative (OS), reductive (RS), and nitrosative (NSS) stresses produce carbonylation, glycation, glutathionylation, sulfhydration, nitration, and nitrosylation reactions. OS, RS, and NSS are interrelated since RS results from an overactivation of antioxidant systems and NSS is the result of the overactivation of the oxidation of nitric oxide (NO). Here, we discuss the general characteristics of the three types of stress and the way by which the reactions they induce (a) damage the DNA structure causing strand breaks or inducing the formation of 8-oxo-d guanosine; (b) modify histones; (c) modify the activities of the enzymes that determine the establishment of epigenetic cues such as DNA methyl transferases, histone methyl transferases, acetyltransferases, and deacetylases; (d) alter DNA reparation enzymes by posttranslational mechanisms; and (e) regulate the activities of intracellular enzymes participating in metabolic reactions and in signaling pathways through posttranslational modifications. Furthermore, the three types of stress may establish new epigenetic marks through these reactions. The development of cardiometabolic disorders in adult life may be programed since early stages of development by epigenetic cues which may be established or modified by OS, RS, and NSS. Therefore, the three types of stress participate importantly in mediating the impact of the early life environment on later health and heritability. Here, we discuss their impact on cardiometabolic diseases. The epigenetic modifications induced by these stresses depend on union and release of chemical residues on a DNA sequence and/or on amino acid residues in proteins, and therefore, they are reversible and potentially treatable.

Reductive stress in striated muscle cells

Reductive stress is defined as a condition of sustained increase in cellular glutathione/glutathione disulfide and NADH/NAD+ ratios. Reductive stress is emerging as an important pathophysiological event in several diseased states, being as detrimental as is oxidative stress. Occurrence of reductive stress has been documented in several cardiomyopathies and is an important pathophysiological factor particularly in coronary artery disease and myocardial infarction. Excess activation of the transcription factor, Nrf2-the master regulator of the antioxidant response-, consequent in most cases to defective autophagy, can lead to reductive stress. In addition, hyperglycemia-induced activation of the polyol pathway can lead to increased NADH/NAD+ ratio, which might translate into increased levels of hydrogen sulfide-via enhanced activity of cystathionine β-synthase-that would fuel reductive stress through inhibition of mitochondrial complex I. Reductive stress may be either a potential weapon against cancer priming tumor cells to apoptosis or a cancer's ally promoting tumor cell proliferation and making tumor cells resistant to reactive oxygen species-inducing drugs. In non-cancer pathological states reductive stress is definitely harmful paradoxically leading to reactive oxygen species overproduction via excess NADPH oxidase 4 activity. In face of the documented occurrence of reductive stress in several heart diseases, there is much less information about the occurrence and effects of reductive stress in skeletal muscle tissue. In the present review we describe relevant results emerged from studies of reductive stress in the heart and review skeletal muscle conditions in which reductive stress has been experimentally documented and those in which reductive stress might have an as yet unrecognized pathophysiological role. Establishing whether reductive stress has a (patho)physiological role in skeletal muscle will hopefully contribute to answer the question whether antioxidant supplementation to the general population, athletes, and a large cohort of patients (e.g. heart, sarcopenic, dystrophic, myopathic, cancer, and bronco-pulmonary patients) is harmless or detrimental.

Reductive Stress Causes Pathological Cardiac Remodeling and Diastolic Dysfunction

Aims: Redox homeostasis is tightly controlled and regulates key cellular signaling pathways. The cell's antioxidant response provides a natural defense against oxidative stress, but excessive antioxidant generation leads to reductive stress (RS). This study elucidated how chronic RS, caused by constitutive activation of nuclear erythroid related factor-2 (caNrf2)-dependent antioxidant system, drives pathological myocardial remodeling. Results: Upregulation of antioxidant transcripts and proteins in caNrf2-TG hearts (TGL and TGH; transgenic-low and -high) dose dependently increased glutathione (GSH) redox potential and resulted in RS, which over time caused pathological cardiac remodeling identified as hypertrophic cardiomyopathy (HCM) with abnormally increased ejection fraction and diastolic dysfunction in TGH mice at 6 months of age. While the TGH mice exhibited 60% mortality at 18 months of age, the rate of survival in TGL was comparable with nontransgenic (NTG) littermates. Moreover, TGH mice had severe cardiac remodeling at ∼6 months of age, while TGL mice did not develop comparable phenotypes until 15 months, suggesting that even moderate RS may lead to irreversible damages of the heart over time. Pharmacologically blocking GSH biosynthesis using BSO (l-buthionine-SR-sulfoximine) at an early age (∼1.5 months) prevented RS and rescued the TGH mice from pathological cardiac remodeling. Here we demonstrate that chronic RS causes pathological cardiomyopathy with diastolic dysfunction in mice due to sustained activation of antioxidant signaling. Innovation and Conclusion: Our findings demonstrate that chronic RS is intolerable and adequate to induce heart failure (HF). Antioxidant-based therapeutic approaches for human HF should consider a thorough evaluation of redox state before the treatment.

Reductive Stress-Induced Mitochondrial Dysfunction and Cardiomyopathy

The goal of this review was to summarize reported studies focusing on cellular reductive stress-induced mitochondrial dysfunction, cardiomyopathy, dithiothreitol- (DTT-) induced reductive stress, and reductive stress-related free radical reactions published in the past five years. Reductive stress is considered to be a double-edged sword in terms of antioxidation and disease induction. As many underlying mechanisms are still unclear, further investigations are obviously warranted. Nonetheless, reductive stress is thought to be caused by elevated levels of cellular reducing power such as NADH, glutathione, and NADPH; and this area of research has attracted increasing attention lately. Albeit, we think there is a need to conduct further studies in identifying more indicators of the risk assessment and prevention of developing heart damage as well as exploring more targets for cardiomyopathy treatment. Hence, it is expected that further investigation of underlying mechanisms of reductive stress-induced mitochondrial dysfunction will provide novel insights into therapeutic approaches for ameliorating reductive stress-induced cardiomyopathy.

Aberrant Upregulation of Compensatory Redox Molecular Machines May Contribute to Sperm Dysfunction in Infertile Men with Unilateral Varicocele: A Proteomic Insight

Aims: To understand the molecular pathways involved in oxidative stress (OS)-mediated sperm dysfunction against a hypoxic and hyperthermic microenvironment backdrop of varicocele through a proteomic approach. Results: Protein selection (261) based on their role in redox homeostasis and/or oxidative/hyperthermic/hypoxic stress response from the sperm proteome data set of unilateral varicocele (UV) in comparison with fertile control displayed 85 to be differentially expressed. Upregulation of cellular oxidant detoxification and glutathione and reduced nicotinamide adenine dinucleotide (NADH) metabolism accompanied with downregulation of protein folding, energy metabolism, and heat stress responses were observed in the UV group. Ingenuity pathway analysis (IPA) predicted suppression of oxidative phosphorylation (OXPHOS) (validated by Western blotting [WB]) along with augmentation in OS and mitochondrial dysfunction in UV. The top affected networks indicated by IPA involved heat shock proteins (HSPs: HSPA2 and HSP90B1). Their expression profile was corroborated by immunocytochemistry and WB. Hypoxia-inducible factor 1A as an upstream regulator of HSPs was predicted by MetaCore. Occurrence of reductive stress in UV spermatozoa was corroborated by thiol redox status. Innovation: This is the first evidence of a novel pathway showing aberrant redox homeostasis against chronic hypoxic insult in varicocele leading to sperm dysfunction. Conclusions: Upregulation of antioxidant system and dysfunctional OXPHOS would have shifted the redox balance of biological redox couples (GSH/GSSG, NAD⁺/NADH, and NADP⁺/NADPH) to a more reducing state leading to reductive stress. Chronic reductive stress-induced OS may be involved in sperm dysfunction in infertile men with UV, where the role of HSPs cannot be ignored. Intervention with antioxidant therapy warrants proper prior investigation.

Biothiol-Activatable Bioluminescent Coelenterazine Derivative for Molecular Imaging in Vitro and in Vivo

There is a high demand for sensitive biothiol probes targeting cysteine, glutathione, and homocysteine. These biothiols are known as playing essential roles to maintain homeostasis and work as indicators of many diseases. This work presents a bioluminescent probe (named AMCM) to detect biothiols in live mammalian cells and in vivo with a limit of detection of 0.11 μM for cysteine in solution and high selectivity for biothiols, making it suitable for real-time biothiol detection in biological systems. Upon application to live cells, AMCM showed low cytotoxicity and sensitively reported bioluminescence in response to changes of biothiol levels. Furthermore, a bioluminescence resonance energy transfer system consisting of AMCM combined with the near-infrared fluorescent protein iRFP713 was applied to in vivo imaging, with emitted tissue-permeable luminescence in living mice. In summary, this work demonstrates that AMCM is of high practical value for the detection of biothiols in living cells and for deep tissue imaging in living animals.

Monitoring NAD(P)H by an ultrasensitive fluorescent probe to reveal reductive stress induced by natural antioxidants in HepG2 cells under hypoxia

An ultrasensitive fluorescent probe for monitoring NAD(P)H and revealing reductive stress induced by natural antioxidants in HepG2 cells under hypoxia.

Reductive stress, the opposite of oxidative stress, represents a disorder in the redox balance state which is harmful to biological systems. For decades, the role of oxidative stress in tumor therapy has been the focus of attention, while the effects of reductive stress have been rarely studied. Here, we report the anti-cancer effects of reductive stress induced by three natural antioxidants (resveratrol, curcumin and celastrol). Considering the fact that the solid tumor microenvironment suffers from hypoxia, we performed cell experiments under hypoxic conditions. In order to observe the reductive stress, we first developed an ultrasensitive fluorescent probe (TCF-MQ) for specifically imaging NAD(P)H which is a marker of reductive stress. TCF-MQ responded to NAD(P)H rapidly and exhibited high sensitivity with a detection limit of 6 nM. With the help of TCF-MQ, we found that upon the treatment of HepG2 cells with pharmacological doses of three natural antioxidants under hypoxic conditions, high levels of NAD(P)H were produced before cell death. The excess NAD(P)H resulted in reductive stress instead of oxidative stress. In contrast, under normoxic conditions, there was no reductive stress involved in the process of cell death induced by three natural antioxidants. Therefore, we hypothesize that the mechanism of cancer cell death induced by natural antioxidants under hypoxia should be attributed to the reductive stress.

Ascorbic acid induced HepG2 cells' apoptosis via intracellular reductive stress

Goals: Destruction of the redox balance in tumor cells is of great significance for triggering their apoptosis in clinical applications. We designed a pH sensitive multifunctional drug nanocarrier with controllable release of ascorbic acid under hypoxic environment to induce tumor cells' apoptosis via enhancing reductive stress, thereby dealing minimum damage to normal tissues. Methods: A core-shell nanostructure of CdTe quantum dots with mesoporous silica coating was developed and functionalized with poly(2-vinylpyridine)-polyethylene glycol-folic acid, which achieves cancer cells' targeting delivery and reversibly pH controlled release of ascorbic acid both in vitro and in vivo. Results: The result demonstrated that ascorbic acid can indeed lead liver cancer cells' death with the increase of nicotinamide adenine dinucleotide phosphate, while normal cells not being affected. The molecular mechanism of apoptosis induced by ascorbic acid was firstly elucidated at cellular levels, and further confirmed via in vivo investigations. Conclusion: For the first time we proposed the concept for applying reductive stress into cancer treatments, which brings great advantage of toxicity free and less damage to normal tissues. In general, this technique has taken an important step in the development of a targeted tumor treatment system, providing perspectives for the design of medicines via reductive stress, and offers new insights into future clinical mild-therapies.

H2Se Induces Reductive Stress in HepG2 Cells and Activates Cell Autophagy by Regulating the Redox of HMGB1 Protein under Hypoxia

Rationale: Selenium has been shown to have chemotherapeutic effects against cancer. However, the anti-cancer mechanism of selenium is not fully understood, and the role of hydrogen selenide (H₂Se), which is a common metabolite of dietary selenium compounds, has not been elucidated due to the lack of detection methods. In this study, we revealed a new anti-cancer mechanism of selenite with the help of a H₂Se fluorescent probe.

Methods: HepG2 cells were cultured under a simulated tumor hypoxic microenvironment. The H₂Se and H₂O₂ levels were detected by fluorescent probes in living cells and in mice. Autophagic and apoptotic proteins were detected by Western blotting. The redox of HMGB1 protein were analyzed by non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis.

Results: After pharmacological doses of Na₂SeO₃ treatment of HepG2 cells under hypoxic conditions, high levels of H₂Se were produced before cell death. The H₂Se accumulation resulted in reductive stress instead of oxidative stress, which was induced by Na₂SeO₃ treatment under normoxic conditions. Furthermore, H₂Se targeted the HMGB1 protein and induced cell autophagy. H₂Se could interrupt the disulfide bond in HMGB1 and promote its secretion. The reduced HMGB1 outside the cells stimulated cell autophagy by inhibiting the Akt/mTOR axis. Here, autophagy played a dual role, i.e., mild autophagy inhibited apoptosis, while excessive autophagy led to autophagy-associated cell death.

Conclusions: These results show that H₂Se plays a key role during HepG2 cell death induced by selenite. Our findings reveal a new anti-cancer mechanism of selenite and provide a new research area for selenium studies.

High doses of synthetic antioxidants induce premature senescence in cultivated mesenchymal stem cells

Stress-induced premature senescence program is known to be activated in cells by various genotoxic stressors, and oxidative stress is considered to be the main of those. To this end, many studies discover antioxidants as protective anti-aging agents. In the current study, we examined the effects of different antioxidants (Tempol, resveratrol, NAC, DPI) on the mesenchymal stem cells maintained in normal physiological conditions. We used high, but non-cytotoxic antioxidant doses which are widely used in laboratory practice to protect cells from oxidative damage. We show that these substances induce reversible block of cell proliferation and do not cause any genotoxic effects when applied to the quiescent cells. However, the same doses of the same substances, when applied to the proliferating cells, can induce irreversible cell cycle arrest, DNA strand breaks accumulation and DNA damage response activation. As a consequence, antioxidant-induced DNA damage results in the stress-induced premature senescence program activation. We conclude that high doses of antioxidants, when applied to the proliferating cells that maintain physiological levels of reactive oxygen species, can cause DNA damage and induce premature senescence which suggests to re-estimate believed unconditional anti-aging antioxidant properties.

Omega 3 rich diet modulates energy metabolism via GPR120-Nrf2 crosstalk in a novel antioxidant mouse model

With obesity rates reaching epidemic proportions, more studies concentrated on reducing the risk and treating this epidemic are vital. Redox stress is an important metabolic regulator involved in the pathophysiology of cardiovascular disease, Type 2 diabetes, and obesity. Oxygen and nitrogen-derived free radicals alter glucose and lipid homeostasis in key metabolic tissues, leading to increases in risk of developing metabolic syndrome. Oxidants derived from dietary fat differ in their metabolic regulation, with numerous studies showing benefits from a high omega 3 rich diet compared to the frequently consumed "western diet" rich in saturated fat. Omega 3 (OM3) fatty acids improve lipid profile, lower inflammation, and ameliorate insulin resistance, possibly through maintaining redox homeostasis. This study is based on the hypothesis that altering endogenous antioxidant production and/or increasing OM3 rich diet consumption will improve energy metabolism and maintain insulin sensitivity. We tested the comparative metabolic effects of a diet rich in saturated fat (HFD) and an omega 3-enriched diet (OM3) in the newly developed 'stress-less' mice model that overexpresses the endogenous antioxidant catalase. Eight weeks of dietary intervention showed that mice overexpressing endogenous catalase compared to their wild-type controls when fed an OM3 enriched diet, in contrast to HFD, activated GPR120-Nrf2 cross-talk to maintain balanced energy metabolism, normal circadian rhythm, and insulin sensitivity. These findings suggest that redox regulation of GPR120/FFAR4 might be an important target in reducing risk of metabolic syndrome and associated diseases.

Heat-shock protein B1 upholds the cytoplasm reduced state to inhibit activation of the Hippo pathway in H9c2 cells

Heat-shock protein B1 (HSPB1) is a multifunctional protein that protects against oxidative stress; however, its function in antioxidant pathways remains largely unknown. Here, we sought to determine the roles of HSPB1 in H9c2 cells subjected to oxidative stress. Using nonreducing sodium dodecyl sulfate polyacrylamide gel electrophoresis, we found that increased HSPB1 expression promoted the reduced states of glutathione reductase (GR), peroxiredoxin 1 (Prx1), and thioredoxin 1, whereas knockdown of HSPB1 attenuated these responses following oxidative stress. Increased HSPB1 expression promoted the activation of GR and thioredoxin reductase. Conversely, knockdown of HSPB1 attenuated these responses following oxidative stress. Importantly, overexpression of HSPB1 promoted the complex formation between HSPB1 and oxidized Prx1, leading to dephosphorylation of STE-mammalian STE20-like kinase 1 (MST1) in H9c2 cells exposed to H₂ O ₂ , whereas downregulation of HSPB1 induced the opposite results. Mechanistically, HSPB1 regulated the Hippo pathway by enhancing the dephosphorylation of MST1, resulting in reduced phosphorylation of LATS1 and Yes-associated protein (YAP). Moreover, HSPB1 regulated YAP-dependent gene expression. Thus, HSPB1 promoted the reduced state of endogenous antioxidant pathways following oxidative stress in H9c2 cells and improved the redox state of the cytoplasm via modulation of the Hippo signaling pathway.

Cardiac-specific overexpression of aldehyde dehydrogenase 2 exacerbates cardiac remodeling in response to pressure overload

Pathological cardiac remodeling during heart failure is associated with higher levels of lipid peroxidation products and lower abundance of several aldehyde detoxification enzymes, including aldehyde dehydrogenase 2 (ALDH2). An emerging idea that could explain these findings concerns the role of electrophilic species in redox signaling, which may be important for adaptive responses to stress or injury. The purpose of this study was to determine whether genetically increasing ALDH2 activity affects pressure overload-induced cardiac dysfunction. Mice subjected to transverse aortic constriction (TAC) for 12 weeks developed myocardial hypertrophy and cardiac dysfunction, which were associated with diminished ALDH2 expression and activity. Cardiac-specific expression of the human ALDH2 gene in mice augmented myocardial ALDH2 activity but did not improve cardiac function in response to pressure overload. After 12 weeks of TAC, ALDH2 transgenic mice had larger hearts than their wild-type littermates and lower capillary density. These findings show that overexpression of ALDH2 augments the hypertrophic response to pressure overload and imply that downregulation of ALDH2 may be an adaptive response to certain forms of cardiac pathology.

Evidence for a hyper-reductive redox in a sub-set of heart failure patients

BACKGROUND

Oxidative stress has been linked to heart failure (HF) in humans. Antioxidant-based treatments are often ineffective. Therefore, we hypothesize that some of the HF patients might have a reductive stress (RS) condition. Investigating RS-related mechanisms will aid in personalized optimization of redox homeostasis for better outcomes among HF patients.

METHODS

Blood samples were collected from HF patients (n = 54) and healthy controls (n = 42) and serum was immediately preserved in - 80 °C for redox analysis. Malondialdehyde (MDA; lipid peroxidation) levels by HPLC, reduced glutathione (GSH) and its redox ratio (GSH/GSSG) using enzymatic-recycling assay in the serum of HF patients were measured. Further, the activities of key antioxidant enzymes were analyzed by UV-Vis spectrophotometry. Non-invasive echocardiography was used to relate circulating redox status with cardiac function and remodeling.

RESULTS

The circulatory redox state (GSH/MDA ratio) was used to stratify the HF patients into normal redox (NR), hyper-oxidative (HO), and hyper-reductive (HR) groups. While the majority of the HF patients exhibited the HO (42%), 41% of them had a normal redox (NR) state. Surprisingly, a subset of HF patients (17%) belonged to the hyper-reductive group, suggesting a strong implication for RS in the progression of HF. In all the groups of HF patients, SOD, GPx and catalase were significantly increased while GR activity was significantly reduced relative to healthy controls. Furthermore, echocardiography analyses revealed that 55% of HO patients had higher systolic dysfunction while 62.5% of the hyper-reductive patients had higher diastolic dysfunction.

CONCLUSION

These results suggest that RS may be associated with HF pathogenesis for a subset of cardiac patients. Thus, stratification of HF patients based on their circulating redox status may serve as a useful prognostic tool to guide clinicians designing personalized antioxidant therapies.

Extending roGFP Emission via Förster-Type Resonance Energy Transfer Relay Enables Simultaneous Dual Compartment Ratiometric Redox Imaging in Live Cells

Reactive oxygen species (ROS) mediate both intercellular and intraorganellar signaling, and ROS propagate oxidative stress between cellular compartments such as mitochondria and the cytosol. Each cellular compartment contains its own sources of ROS as well as antioxidant mechanisms, which contribute to dynamic fluctuations in ROS levels that occur during signaling, metabolism, and stress. However, the coupling of redox dynamics between cellular compartments has not been well studied because of the lack of available sensors to simultaneously measure more than one subcellular compartment in the same cell. Currently, the redox-sensitive green fluorescent protein, roGFP, has been used extensively to study compartment-specific redox dynamics because it provides a quantitative ratiometric readout and it is amenable to subcellular targeting as a genetically encoded sensor. Here, we report a new family of genetically encoded fluorescent protein sensors that extend the fluorescence emission of roGFP via Förster-type resonance energy transfer to an acceptor red fluorescent protein for dual-color live-cell microscopy. We characterize the redox and optical properties of the sensor proteins, and we demonstrate that they can be used to simultaneously measure cytosolic and mitochondrial ROS in living cells. Furthermore, we use these sensors to reveal cell-to-cell heterogeneity in redox coupling between the cytosol and mitochondria when neuroblastoma cells are exposed to reductive and metabolic stresses.

Reductive Stress in Inflammation-Associated Diseases and the Pro-Oxidant Effect of Antioxidant Agents

Abstract: Reductive stress (RS) is the counterpart oxidative stress (OS), and can occur in response to conditions that shift the redox balance of important biological redox couples, such as the NAD⁺/NADH, NADP⁺/NADPH, and GSH/GSSG, to a more reducing state. Overexpression of antioxidant enzymatic systems leads to excess reducing equivalents that can deplete reactive oxidative species, driving the cells to RS. A feedback regulation is established in which chronic RS induces OS, which in turn, stimulates again RS. Excess reducing equivalents may regulate cellular signaling pathways, modify transcriptional activity, induce alterations in the formation of disulfide bonds in proteins, reduce mitochondrial function, decrease cellular metabolism, and thus, contribute to the development of some diseases in which NF-κB, a redox-sensitive transcription factor, participates. Here, we described the diseases in which an inflammatory condition is associated to RS, and where delayed folding, disordered transport, failed oxidation, and aggregation are found. Some of these diseases are aggregation protein cardiomyopathy, hypertrophic cardiomyopathy, muscular dystrophy, pulmonary hypertension, rheumatoid arthritis, Alzheimer's disease, and metabolic syndrome, among others. Moreover, chronic consumption of antioxidant supplements, such as vitamins and/or flavonoids, may have pro-oxidant effects that may alter the redox cellular equilibrium and contribute to RS, even diminishing life expectancy.

Identification of transcriptome signature for myocardial reductive stress

The nuclear factor erythroid 2 like 2 (Nfe2l2/Nrf2) is a master regulator of antioxidant gene transcription. We recently identified that constitutive activation of Nrf2 (CaNrf2) caused reductive stress (RS) in the myocardium. Here we investigate how chronic Nrf2 activation alters myocardial mRNA transcriptome in the hearts of CaNrf2 transgenic (TG-low and TG-high) mice using an unbiased integrated systems approach and next generation RNA sequencing followed by qRT-PCR methods. A total of 246 and 1031 differentially expressed genes (DEGs) were identified in the heart of TGL and TGH in relation to NTG littermates at ~ 6 months of age. Notably, the expression and validation of the transcripts were gene-dosage dependent and statistically significant. Ingenuity Pathway Analysis identified enriched biological processes and canonical pathways associated with myocardial RS in the CaNrf2-TG mice. In addition, an overrepresentation of xenobiotic metabolic signaling, glutathione-mediated detoxification, unfolded protein response, and protein ubiquitination was observed. Other, non-canonical signaling pathways identified include: eNOS, integrin-linked kinase, glucocorticoid receptor, PI3/AKT, actin cytoskeleton, cardiac hypertrophy, and the endoplasmic reticulum stress response. In conclusion, this mRNA profiling identified a "biosignature" for pro-reductive (TGL) and reductive stress (TGH) that can predict the onset, rate of progression, and clinical outcome of Nrf2-dependent myocardial complications. We anticipate that this global sequencing analysis will illuminate the undesirable effect of chronic Nrf2 signaling leading to RS-mediated pathogenesis besides providing important guidance for the application of Nrf2 activation-based cytoprotective strategies.

Safety assessment of the dietary supplement OxyELITE™ Pro (New Formula) in inbred and outbred mouse strains

Herbal dietary supplements have gained wide acceptance as alternatives to conventional therapeutic agents despite concerns regarding their efficacy and safety. In 2013, a spate of severe liver injuries across the United States was linked to the dietary supplement OxyELITE Pro-New Formula (OEP-NF), a multi-ingredient product marketed for weight loss and exercise performance enhancement. The principal goal of this study was to assess the hepatotoxic potential of OEP-NF in outbred and inbred mouse models. In an acute toxicity study, significant mortality was observed after administering 10X and 3X mouse-equivalent doses (MED) of OEP-NF, respectively. Increases in liver/body weight ratio, ALT and AST were observed in female B6C3F₁ mice after gavaging 2X and 1.5X MED of OEP-NF. Similar findings were observed in a 90-day feeding study. These alterations were paralleled by altered expression of gene- and microRNA-signatures of hepatotoxicity, including Cd36, Nqo1, Aldoa, Txnrd1, Scd1 and Ccng1, as well as miR-192, miR-193a and miR-125b and were most pronounced in female B6C3F₁ mice. Body weight loss, observed at week 1, was followed by weight gain throughout the feeding studies. These findings bolster safety and efficacy concerns for OEP-NF, and argue strongly for implementation of pre-market toxicity studies within the dietary supplement industry.

Divergent roles of endothelial nitric oxide synthases system in maintaining cardiovascular homeostasis

Accumulating evidence has demonstrated the importance of reactive oxygen species (ROS) as an essential second messenger in health and disease. Endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases, in which pathological levels of ROS are substantially involved. The endothelium plays a crucial role in modulating tone of underlying vascular smooth muscle by synthesizing and releasing nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors in a distinct vessel size-dependent manner through the diverse roles of the endothelial NO synthases (NOSs) system. Endothelium-derived hydrogen peroxide (H₂O₂) is a physiological signaling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular homeostasis. In the clinical settings, it has been reported that antioxidant supplements are unexpectedly ineffective to prevent cardiovascular events. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂O₂/EDH through the diverse functions of endothelial NOSs system in maintaining cardiovascular homeostasis. A better understanding of cardiovascular redox signaling is certainly needed to develop novel therapeutic strategies in cardiovascular medicine. In this review, we will briefly summarize the current knowledge on the emerging regulatory roles of redox signaling pathways in cardiovascular homeostasis, with particular focus on the two endothelial NOSs-derived mediators, NO and H₂O₂/EDH.