The expanding network of redox signaling: new observations, complexities, and perspectives

High Fructose Intake and Adipogenesis

In modern societies, high fructose intake from sugar-sweetened beverages has contributed to obesity development. In the diet, sucrose and high fructose corn syrup are the main sources of fructose and can be metabolized in the intestine and transported into the systemic circulation. The liver can metabolize around 70% of fructose intake, while the remaining is metabolized by other tissues. Several tissues including adipose tissue express the main fructose transporter GLUT5. In vivo, chronic fructose intake promotes white adipose tissue accumulation through activating adipogenesis. In vitro experiments have also demonstrated that fructose alone induces adipogenesis by several mechanisms, including (1) triglycerides and very-low-density lipoprotein (VLDL) production by fructose metabolism, (2) the stimulation of glucocorticoid activation by increasing 11β-HSD1 activity, and (3) the promotion of reactive oxygen species (ROS) production through uric acid, NOX and XOR expression, mTORC1 signaling and Ang II induction. Moreover, it has been observed that fructose induces adipogenesis through increased ACE2 expression, which promotes high Ang-(1-7) levels, and through the inhibition of the thermogenic program by regulating Sirt1 and UCP1. Finally, microRNAs may also be involved in regulating adipogenesis in high fructose intake conditions. In this paper, we propose further directions for research in fructose participation in adipogenesis.

The cytotoxic effects of dimethyl sulfoxide in mouse preimplantation embryos: a mechanistic study

Rationale: Dimethyl sulfoxide (DMSO) is commonly used as a solvent for water-insoluble substances, a vehicle for drug therapy, and a cryoprotectant for cultured cells. DMSO induced embryonic defects and its mechanism of action remains unclear. The rationale is based on the assumption that DMSO supplementation should induce long-term negative effects on both pre- and post-implantation embryo development.

Methods: DMSO induced oxidative stress, ER stress, autophagy, mitophagy, signaling responsible genes and proteins were determined by RT-qPCR, Western blotting, immunofluorescence, and confocal microscopy. DMSO induced mitochondrial dysfunction was measured by transmission electron microcopy and JC-1 assay. Apoptosis was estimated using TUNEL and comet assay. Post-implantation embryo developmental capability was estimated by implantation site and fetus numbers.

Results: Exposure to DMSO induced an early oxidative stress response within 0.5 to 2 h in 1-cell zygotes by disrupting the balance of pro- and anti-oxidants. Notably, DMSO-treated 2-cell embryos showed increased expression of unfolded protein response genes such as Hspa5, Hsp90b1, Ddit3, Atf4, and Xbp1. As a result, the development of many embryos is arrested at the 2-cell, 4-cell, or morula stages in a dose-dependent manner. Further, DMSO-induced endoplasmic reticulum stress increased mitochondrial Ca²⁺ levels, induced mitochondrial depolarization/dysfunction, and induced apoptotic cell death via the JNK/ATF2-dependent pathway. Consequently, treatment with DMSO increased the expression of autophagy initiation-, phagophore elongation-, and autophagosome formation-related genes, as well as localization of PINK1/Parkin, which are the main mediators of mitophagy, in mitochondria. Interestingly, DMSO causes cytotoxic effects in preimplantation embryos by inducing extensive mitophagy and autophagy. Especially, DMSO treatment decreased the inner cell mass and trophectoderm cell numbers as well as mRNA expression of B3gnt5 and Wnt3a in developed blastocysts, which decreased the implantation and developmental rates of full-term offspring after being transferred into pseudopregnant mice.

Conclusion: These results provide a significant contribution to finding effective protective agents to combat DMSO mediated reproductive toxicity for application in human embryos in the near future.

Diabetes and Kidney Disease: Role of Oxidative Stress

Intrarenal oxidative stress plays a critical role in the initiation and progression of diabetic kidney disease (DKD). Enhanced oxidative stress results from overproduction of reactive oxygen species (ROS) in the context of concomitant, insufficient antioxidant pathways. Renal ROS production in diabetes is predominantly mediated by various NADPH oxidases (NOXs), but a defective antioxidant system as well as mitochondrial dysfunction may also contribute. Recent Advances: Effective agents targeting the source of ROS generation hold the promise to rescue the kidney from oxidative damage and prevent subsequent progression of DKD. Critical Issues and Future Directions: In the present review, we summarize and critically analyze molecular and cellular mechanisms that have been demonstrated to be involved in NOX-induced renal injury in diabetes, with particular focus on the role of increased glomerular injury, the development of albuminuria, and tubulointerstitial fibrosis, as well as mitochondrial dysfunction. Furthermore, novel agents targeting NOX isoforms are discussed. Antioxid. Redox Signal. 25, 657-684.

NADPH oxidases as therapeutic targets in ischemic stroke

Reactive oxygen species (ROS) act physiologically as signaling molecules. In pathological conditions, such as ischemic stroke, ROS are released in excessive amounts and upon reperfusion exceed the body's antioxidant detoxifying capacity. This process leads to brain tissue damage during reoxygenation. Consequently, antioxidant strategies have long been suggested as a therapy for experimental stroke, but clinical trials have not yet been able to promote the translation of this concept into patient treatment regimens. As an evolution of this concept, recent studies have targeted the sources of ROS generation-rather than ROS themselves. In this context, NADPH oxidases have been identified as important generators of ROS in the cerebral vasculature under both physiological conditions in general and during ischemia/reoxygenation in particular. Inhibition of NADPH oxidases or genetic deletion of certain NADPH oxidase isoforms has been found to considerably reduce ischemic injury in experimental stroke. This review focuses on recent advances in the understanding of NADPH oxidase-mediated tissue injury in the cerebral vasculature, particularly at the level of the blood-brain barrier, and highlights promising inhibitory strategies that target the NADPH oxidases.

Partial restoration of cardio-vascular defects in a rescued severe model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a leading genetic cause of infantile death. Loss of a gene called Survival Motor Neuron 1 (SMN1) and, as a result, reduced levels of the Survival Motor Neuron (SMN) protein leads to SMA development. SMA is characterized by the loss of functional motor neurons in the spinal cord. However, accumulating evidence suggests the contribution of other organs to the composite SMA phenotype and disease progression. A growing number of congenital heart defects have been identified in severe SMA patients. Consistent with the clinical cases, we have recently identified developmental and functional heart defects in two SMA mouse models, occurring at embryonic stage in a severe SMA model and shortly after birth in a less severe model (SMN∆7). Our goal was to examine the late stage cardiac abnormalities in untreated SMN∆7 mice and to determine whether gene replacement therapy restores cardiac structure/function in rescued SMN∆7 model. To reveal the extent of the cardiac structural/functional repair in the rescued mice, we analyzed the heart of untreated and treated SMN∆7 model using self-complementary Adeno-associated virus (serotype 9) expressing the full-length SMN cDNA. We examined the characteristics of the heart failure such as remodeling, fibrosis, oxidative stress, and vascular integrity in both groups. Our results clearly indicate that fibrosis, oxidative stress activation, vascular remodeling, and a significant decrease in the number of capillaries exist in the SMA heart. The cardiac structural defects were improved drastically in the rescued animals, however, the level of impairment was still significant compared to the age-matched wildtype littermates. Furthermore, functional analysis by in vivo cardiac magnetic resonance imaging (MRI) revealed that the heart of the treated SMA mice still exhibits functional defects. In conclusion, cardiac abnormalities are only partially rescued in post-birth treated SMA animals and these abnormalities may contribute to the premature death of vector-treated SMA animals with seemingly rescued motor function but an average life span of less than 70 days as reported in several studies.

Redox mechanisms in hepatic chronic wound healing and fibrogenesis

Reactive oxygen species (ROS) generated within cells or, more generally, in a tissue environment, may easily turn into a source of cell and tissue injury. Aerobic organisms have developed evolutionarily conserved mechanisms and strategies to carefully control the generation of ROS and other oxidative stress-related radical or non-radical reactive intermediates (that is, to maintain redox homeostasis), as well as to 'make use' of these molecules under physiological conditions as tools to modulate signal transduction, gene expression and cellular functional responses (that is, redox signalling). However, a derangement in redox homeostasis, resulting in sustained levels of oxidative stress and related mediators, can play a significant role in the pathogenesis of major human diseases characterized by chronic inflammation, chronic activation of wound healing and tissue fibrogenesis. This review has been designed to first offer a critical introduction to current knowledge in the field of redox research in order to introduce readers to the complexity of redox signalling and redox homeostasis. This will include ready-to-use key information and concepts on ROS, free radicals and oxidative stress-related reactive intermediates and reactions, sources of ROS in mammalian cells and tissues, antioxidant defences, redox sensors and, more generally, the major principles of redox signalling and redox-dependent transcriptional regulation of mammalian cells. This information will serve as a basis of knowledge to introduce the role of ROS and other oxidative stress-related intermediates in contributing to essential events, such as the induction of cell death, the perpetuation of chronic inflammatory responses, fibrogenesis and much more, with a major focus on hepatic chronic wound healing and liver fibrogenesis.

Keeping the engine primed: HIF factors as key regulators of cardiac metabolism and angiogenesis during ischemia

Myocardial ischemia, the most common cause of cardiac hypoxia in clinical medicine, occurs when oxygen delivery cannot meet myocardial metabolic requirements in the heart. This deficiency can result from either a reduced supply of oxygen (decreased coronary bloodflow) or an increased myocardial demand for oxygen (increased wall stress or afterload). Patients with stable coronary artery disease as well as patients experiencing acute myocardial infarction can experience episodes of severe ischemia. Although hypoxia is an obligatory component, it is not the sole environmental stress experienced by the ischemic heart. Reperfusion after ischemia is associated with increased oxidative stress as the heart reverts to aerobic respiration and thereby generates toxic levels of reactive oxygen species (ROS). During mild ischemia, mitochondrial function is partially compromised and substrate preferences adapt to sustain adequate ATP generation. With severe ischemia, mitochondrial function is markedly compromised and anaerobic metabolism must provide energy no matter what the cost in generation of toxic ROS adducts. Ischemia produces a variety of environmental stresses that impair cardiovascular function. As a result, multiple signaling pathways are activated in mammalian cells during ischemia/reperfusion injury in an attempt to minimize cellular injury and maintain cardiac output. Amongst the transcriptional regulators activated are members of the hypoxia inducible factor (HIF) transcription factor family. HIF factors regulate a variety of genes that affect a myriad of cellular processes including metabolism, angiogenesis, cell survival, and oxygen delivery, all of which are important in the heart. In this review, we will focus on the metabolic and angiogenic aspects of HIF biology as they relate to the heart during ischemia. We will review the metabolic requirements of the heart under normal as well as hypoxic conditions, the effects of preconditioning and its regulation as it pertains to HIF biology, the apparent roles of HIF-1 and HIF-2 in intermediary metabolism, and translational applications of HIF-1 and HIF-2 biology to cardiac angiogenesis. Increased understanding of the role of HIFs in cardiac ischemia will ultimately influence clinical cardiovascular practice.

Effects of biological oxidants on the catalytic activity and structure of group VIA phospholipase A2

Group VIA phospholipase A(2) (iPLA(2)beta) is expressed in phagocytes, vascular cells, pancreatic islet beta-cells, neurons, and other cells and plays roles in transcriptional regulation, cell proliferation, apoptosis, secretion, and other events. A bromoenol lactone (BEL) suicide substrate used to study iPLA(2)beta functions inactivates iPLA(2)beta by alkylating Cys thiols. Because thiol redox reactions are important in signaling and some cells that express iPLA(2)beta produce biological oxidants, iPLA(2)beta might be subject to redox regulation. We report that biological concentrations of H(2)O(2), NO, and HOCl inactivate iPLA(2)beta, and this can be partially reversed by dithiothreitol (DTT). Oxidant-treated iPLA(2)beta modifications were studied by LC-MS/MS analyses of tryptic digests and included DTT-reversible events, e.g., formation of disulfide bonds and sulfenic acids, and others not so reversed, e.g., formation of sulfonic acids, Trp oxides, and Met sulfoxides. W(460) oxidation could cause irreversible inactivation because it is near the lipase consensus sequence ((463)GTSTG(467)), and site-directed mutagenesis of W(460) yields active mutant enzymes that exhibit no DTT-irreversible oxidative inactivation. Cys651-sulfenic acid formation could be one DTT-reversible inactivation event because Cys651 modification correlates closely with activity loss and its mutagenesis reduces sensitivity to inhibition. Intermolecular disulfide bond formation might also cause reversible inactivation because oxidant-treated iPLA(2)beta contains DTT-reducible oligomers, and oligomerization occurs with time- and temperature-dependent iPLA(2)beta inactivation that is attenuated by DTT or ATP. Subjecting insulinoma cells to oxidative stress induces iPLA(2)beta oligomerization, loss of activity, and subcellular redistribution and reduces the rate of release of arachidonate from phospholipids. These findings raise the possibility that redox reactions affect iPLA(2)beta functions.

The principal eosinophil peroxidase product, HOSCN, is a uniquely potent phagocyte oxidant inducer of endothelial cell tissue factor activity: a potential mechanism for thrombosis in eosinophilic inflammatory states

In vivo, bromide (Br(-)), nitrite (NO(2)(-)), and thiocyanate (SCN(-)) compete for oxidation by eosinophil peroxidase (EPO) and H(2)O(2), yielding, respectively, HOBr, NO(2)., and HOSCN. We have recently shown that SCN(-) is the strongly preferred substrate for EPO in vivo and that HOSCN, in contrast with other EPO-generated oxidants and HOCl, is a relatively weak, cell-permeant, sulfhydryl (SH)-reactive oxidant. We here show that HOSCN is a uniquely potent (up to 100-fold) phagocyte oxidant inducer of tissue factor (TF) activity in human umbilical vein endothelial cells (HUVECs). This induction is attributable to transcriptional up-regulation of TF gene expression dependent upon both activation of the p65/c-Rel TF-kappaB transcription factor and activity of the ERK1/2 kinase pathway upstream of Egr-1 and was markedly further enhanced in the presence of wortmannin, an inhibitor of the PI3 kinase/Akt pathway. HOSCN also markedly activates the proinflammatory p65/p50 NF-kappaB pathway. Based on these findings we hypothesize that HOSCN generated by adherent and infiltrating eosinophils may provoke the development of a prothrombotic and proinflammatory endothelial/endocardial phenotype that promotes the pronounced thrombotic diathesis characteristic of the hypereosinophilic syndrome.

Neuronal expression of the NADPH oxidase NOX4, and its regulation in mouse experimental brain ischemia

Ischemia-induced neuronal damage has been linked to elevated production of reactive oxygen species (ROS) both in animal models and in humans. NADPH oxidase enzymes (NOX-es) are a major enzymatic source of ROS, but their role in brain ischemia has not yet been investigated. The present study was carried out to examine the expression of NOX4, one of the new NADPH oxidase isoforms in a mouse model of focal permanent brain ischemia. We demonstrate that NOX4 is expressed in neurons using in situ hybridization and immunohistochemistry. Ischemia, induced by middle cerebral artery occlusion resulted in a dramatic increase in cortical NOX4 expression. Elevated NOX4 mRNA levels were detectable as early as 24 h after the onset of ischemia and persisted throughout the 30 days of follow-up period, reaching a maximum between days 7 and 15. The early onset suggests neuronal reaction, while the peak period corresponds to the time of neoangiogenesis occurring mainly in the peri-infarct region. The occurrence of NOX4 in the new capillaries was confirmed by immunohistochemical staining. In summary, our paper reports the presence of the ROS producing NADPH oxidase NOX4 in neurons and demonstrates an upregulation of its expression under ischemic conditions. Moreover, a role for NOX4 in ischemia/hypoxia-induced angiogenesis is suggested by its prominent expression in newly formed capillaries.

Inhibition of MHC II gene transcription by nitric oxide and antioxidants

MHC class II molecules are expressed on the surface of antigen presenting cells and are loaded with peptides processed from the phagosomal compartment of these cells. Such complexes interact with the CD4 positive T lymphocyte receptor for antigen and a strong interaction is followed by T cell activation and proliferation. As class II expression is critical for antigen specific immunity its expression mostly restricted to a few cell types but can be induced on others in response to interferon gamma. This expansion of antigen presenting ability plays a role in increasing the duration and intensity of the immune response. Nitric oxide and antioxidants attenuate this class II induction through negative effects on the induction of class II transactivator protein expression and on the binding of transcription factor NF-Y to the class II promoter.

Ozone as Janus: this controversial gas can be either toxic or medically useful

Ozone is an intrinsically toxic gas and its hazardous employment has led to a poor consideration of ozone therapy. The aim of this review is to indicate that a wrong dogma and several misconceptions thwart progress: in reality, properly performed ozone therapy, carried out by expert physicians, can be very useful when orthodox medicine appears inadequate. The unbelievable versatility of ozone therapy is due to the cascade of ozone-derived compounds able to act on several targets leading to a multifactorial correction of a pathological state. During the past decade, contrary to all expectations, it has been demonstrated that the judicious application of ozone in chronic infectious diseases, vasculopathies, orthopedics and even dentistry has yielded such striking results that it is deplorable that the medical establishment continues to ignore ozone therapy.

Vanin-1-/- mice exhibit a glutathione-mediated tissue resistance to oxidative stress

Vanin-1 is an epithelial ectoenzyme with pantetheinase activity and generating the amino-thiol cysteamine through the metabolism of pantothenic acid (vitamin B(5)). Here we show that Vanin-1(-/-) mice, which lack cysteamine in tissues, exhibit resistance to oxidative injury induced by whole-body gamma-irradiation or paraquat. This protection is correlated with reduced apoptosis and inflammation and is reversed by treating mutant animals with cystamine. The better tolerance of the Vanin-1(-/-) mice is associated with an enhanced gamma-glutamylcysteine synthetase activity in liver, probably due to the absence of cysteamine and leading to elevated stores of glutathione (GSH), the most potent cellular antioxidant. Consequently, Vanin-1(-/-) mice maintain a more reducing environment in tissue after exposure to irradiation. In normal mice, we found a stress-induced biphasic expression of Vanin-1 regulated via antioxidant response elements in its promoter region. This process should finely tune the redox environment and thus change an early inflammatory process into a late tissue repair process. We propose Vanin-1 as a key molecule to regulate the GSH-dependent response to oxidative injury in tissue at the epithelial level. Therefore, Vanin/pantetheinase inhibitors could be useful for treatment of damage due to irradiation and pro-oxidant inducers.

Triterpenoid electrophiles (avicins) activate the innate stress response by redox regulation of a gene battery

Avicins are proapoptotic and anti-inflammatory triterpene electrophiles isolated from an Australian desert tree, Acacia victoriae. The presence of two alpha,beta unsaturated carbonyl groups (Michael reaction sites) in the side chain of the avicin molecule prompted us to study its effects on NF-E2-related factor 2 (Nrf2), a redox-regulated transcription factor that controls the expression of a battery of detoxification and antioxidant proteins via its binding to antioxidant response element (ARE). Avicin D-treated Hep G2 cells showed translocation of Nrf2 into the nucleus and a time-dependent increase in ARE activity. These properties were sensitive to DTT, suggesting that avicins affect one or more critical cysteine residues, probably on the Keap1 molecule. Downstream of ARE, an activation of a battery of stress-induced proteins occurred. The implications of these findings were evaluated in vivo in mouse skin exposed to an ancient stressor, UV light. Avicins inhibited epidermal hyperplasia, reduced p53 mutation, enhanced apoptosis, decreased generation of 8-hydroxy-2'-deoxyguanosine, and enhanced expression of NADPH:quinone oxidoreductase 1 and heme oxygenase-1. These data, combined with our earlier published work, demonstrate that avicins represent a new class of plant stress metabolites capable of activating stress adaptation and suppressing proinflammatory components of the innate immune system in human cells by redox regulation. The relevance for treatment of clinical diseases in which stress responses are dysfunctional or deficient is discussed.