A Fenton reaction at the endoplasmic reticulum is involved in the redox control of hypoxia-inducible gene expression

Lactate and lactylation in cardiovascular diseases: current progress and future perspectives

Cardiovascular diseases (CVDs) are often linked to structural and functional impairments, such as heart defects and circulatory dysfunction, leading to compromised peripheral perfusion and heightened morbidity risks. Metabolic remodeling, particularly in the context of cardiac fibrosis and inflammation, is increasingly recognized as a pivotal factor in the pathogenesis of CVDs. Metabolic syndromes further predispose individuals to these conditions, underscoring the need to elucidate the metabolic underpinnings of CVDs. Lactate, a byproduct of glycolysis, is now recognized as a key molecule that connects cellular metabolism with the regulation of cellular activity. The transport of lactate between different cells is essential for metabolic homeostasis and signal transduction. Disruptions to lactate dynamics are implicated in various CVDs. Furthermore, lactylation, a novel post-translational modification, has been identified in cardiac cells, where it influences protein function and gene expression, thereby playing a significant role in CVD pathogenesis. In this review, we summarized recent advancements in understanding the role of lactate and lactylation in CVDs, offering fresh insights that could guide future research directions and therapeutic interventions. The potential of lactate metabolism and lactylation as innovative therapeutic targets for CVD is a promising avenue for exploration.

Pterostilbene Induces Apoptosis from Endoplasmic Reticulum Stress Synergistically with Anticancer Drugs That Deposit Iron in Mitochondria

Anticancer agents are playing an increasing role in the treatment of gastric cancer (GC); however, novel anticancer agents have not been fully developed. Therefore, it is important to investigate compounds that improve sensitivity to the existing anticancer drugs. We have reported that pterostilbene (PTE), a plant stilbene, enhances the antitumor effect of low doses of sunitinib in gastric cancer cells accumulating mitochondrial iron (II) (mtFe) at low doses. In this study, we investigated the relationship between the mtFe deposition and the synergistic effect of PTE and different anticancer drugs. For this study, we used 5-fluorouracil (5FU), cisplatin (CPPD), and lapatinib (LAP), which are frequently used in the treatment of GC, and doxorubicin (DOX), which is known to deposit mtFe. A combination of low-dose PTE and these drugs suppressed the expression of PDZ domain-containing 8 (PDZD8) and increased mtFe accumulation and mitochondrial H2O2. Consequently, reactive oxygen species-associated hypoxia inducible factor-1α activation induced endoplasmic reticulum stress and led to apoptosis, but not ferroptosis. In contrast, 5FU and CDDP did not show the same changes as those observed with PTE and DOX or LAP, and there was no synergistic effect with PTE. These results indicate that the combination of PTE with iron-accumulating anticancer drugs exhibits a strong synergistic effect. These findings would help in developing novel therapeutic strategies for GC. However, further clinical investigations are required.

Nanoconfinement-triggered oligomerization pathway for efficient removal of phenolic pollutants via a Fenton-like reaction

Heterogeneous Fenton reaction represents one of the most reliable technologies to ensure water safety, but is currently challenged by the sluggish Fe(III) reduction, excessive input of chemicals for organic mineralization, and undesirable carbon emission. Current endeavors to improve the catalytic performance of Fenton reaction are mostly focused on how to accelerate Fe(III) reduction, while the pollutant degradation step is habitually overlooked. Here, we report a nanoconfinement strategy by using graphene aerogel (GA) to support UiO-66-NH2-(Zr) binding atomic Fe(III), which alters the carbon transfer route during phenol removal from kinetically favored ring-opening route to thermodynamically favored oligomerization route. GA nanoconfinement favors the Fe(III) reduction by enriching the reductive intermediates and allows much faster phenol removal than the unconfined analog (by 208 times in terms of first-order rate constant) and highly efficient removal of total organic carbon, i.e., 92.2 ± 3.7% versus 3.6 ± 0.3% in 60 min. Moreover, this oligomerization route reduces the oxidant consumption for phenol removal by more than 95% and carbon emission by 77.9%, compared to the mineralization route in homogeneous Fe2++H2O2 system. Our findings may upgrade the regulatory toolkit for Fenton reactions and provide an alternative carbon transfer route for the removal of aqueous pollutants.

Self-carbon-thermal-reduction strategy for boosting the Fenton-like activity of single Fe-N4 sites by carbon-defect engineering

Carbon-defect engineering in metal single-atom catalysts by simple and robust strategy, boosting their catalytic activity, and revealing the carbon defect-catalytic activity relationship are meaningful but challenging. Herein, we report a facile self-carbon-thermal-reduction strategy for carbon-defect engineering of single Fe-N4 sites in ZnO-Carbon nano-reactor, as efficient catalyst in Fenton-like reaction for degradation of phenol. The carbon vacancies are easily constructed adjacent to single Fe-N4 sites during synthesis, facilitating the formation of C-O bonding and lowering the energy barrier of rate-determining-step during degradation of phenol. Consequently, the catalyst Fe-NCv-900 with carbon vacancies exhibits a much improved activity than the Fe-NC-900 without abundant carbon vacancies, with 13.5 times improvement in the first-order rate constant of phenol degradation. The Fe-NCv-900 shows high activity (97% removal ratio of phenol in only 5 min), good recyclability and the wide-ranging pH universality (pH range 3-9). This work not only provides a rational strategy for improving the Fenton-like activity of metal single-atom catalysts, but also deepens the fundamental understanding on how periphery carbon environment affects the property and performance of metal-N4 sites.

Protein kinase B/AKT phosphorylates hypoxia-inducible factor-3α1 in response to insulin, promoting cell growth and migration

Hypoxia-inducible factors (HIFs) are best known for their roles in the adaptation to low oxygen environments. Besides hypoxia, HIF-1/2 α-subunits are also regulated by various non-hypoxic stimuli including insulin which can act via the PI3K/protein kinase B (PKB) signaling pathway. However, with respect to insulin little is known about HIF-3α. We aimed to investigate this relationship and found that insulin stimulates HIF-3α expression under both normal and low oxygen conditions. Blocking PKB activity reversed the effects of insulin, indicating that HIF-3α is a direct target of PKB. We identified serine 524, located in the oxygen-dependent degradation domain of HIF-3α, as a phosphorylation site of PKB. Mutating serine 524 impaired binding of PKB to HIF-3α and its ubiquitination, suggesting that PKB regulates HIF-3α stability through phosphorylation, thereby affecting important cellular processes such as cell viability and cell adhesion. Importantly, we discovered that this phosphorylation site also influenced insulin-dependent cell migration. These findings shed light on a novel mechanism by which insulin affects PKB-dependent HIF-3α expression and activity, with potential implications in metabolic diseases and cancer.

Signaling pathways in vascular function and hypertension: molecular mechanisms and therapeutic interventions

Hypertension is a global public health issue and the leading cause of premature death in humans. Despite more than a century of research, hypertension remains difficult to cure due to its complex mechanisms involving multiple interactive factors and our limited understanding of it. Hypertension is a condition that is named after its clinical features. Vascular function is a factor that affects blood pressure directly, and it is a main strategy for clinically controlling BP to regulate constriction/relaxation function of blood vessels. Vascular elasticity, caliber, and reactivity are all characteristic indicators reflecting vascular function. Blood vessels are composed of three distinct layers, out of which the endothelial cells in intima and the smooth muscle cells in media are the main performers of vascular function. The alterations in signaling pathways in these cells are the key molecular mechanisms underlying vascular dysfunction and hypertension development. In this manuscript, we will comprehensively review the signaling pathways involved in vascular function regulation and hypertension progression, including calcium pathway, NO-NOsGC-cGMP pathway, various vascular remodeling pathways and some important upstream pathways such as renin-angiotensin-aldosterone system, oxidative stress-related signaling pathway, immunity/inflammation pathway, etc. Meanwhile, we will also summarize the treatment methods of hypertension that targets vascular function regulation and discuss the possibility of these signaling pathways being applied to clinical work.

The role of hypoxia-inducible factor 1 alpha (HIF-1α) modulation in heavy metal toxicity

Hypoxia-inducible factor 1 (HIF-1) is an oxygen-sensing transcriptional regulator orchestrating a complex of adaptive cellular responses to hypoxia. Several studies have demonstrated that toxic metal exposure may also modulate HIF-1α signal transduction pathway, although the existing data are scarce. Therefore, the present review aims to summarize the existing data on the effects of toxic metals on HIF-1 signaling and the potential underlying mechanisms with a special focus on prooxidant effect of the metals. The particular effect of metals was shown to be dependent on cell type, varying from down- to up-regulation of HIF-1 pathway. Inhibition of HIF-1 signaling may contribute to impaired hypoxic tolerance and adaptation, thus promoting hypoxic damage in the cells. In contrast, its metal-induced activation may result in increased tolerance to hypoxia through increased angiogenesis, thus promoting tumor growth and contributing to carcinogenic effect of heavy metals. Up-regulation of HIF-1 signaling is mainly observed upon Cr, As, and Ni exposure, whereas Cd and Hg may both stimulate and inhibit HIF-1 pathway. The mechanisms underlying the influence of toxic metal exposure on HIF-1 signaling involve modulation of prolyl hydroxylases (PHD2) activity, as well as interference with other tightly related pathways including Nrf2, PI3K/Akt, NF-κB, and MAPK signaling. These effects are at least partially mediated by metal-induced ROS generation. Hypothetically, maintenance of adequate HIF-1 signaling upon toxic metal exposure through direct (PHD2 modulation) or indirect (antioxidant) mechanisms may provide an additional strategy for prevention of adverse effects of metal toxicity.

Inflammatory stimulus worsens the effects of UV-A exposure on J774 cells

UV-A radiation affects skin homeostasis by promoting oxidative distress. Endogenous photosensitizers in the dermis and epidermis of human skin absorb UV-A radiation forming excited states (singlet and triplet) and reactive oxygen species (ROS) producing oxidized compounds that trigger biological responses. The activation of NF-kB induces the expression of pro-inflammatory cytokines and can intensify the generation of ROS. However, there is no studies evaluating the cross talks between inflammatory stimulus and UV-A exposure on the levels of redox misbalance and inflammation. In here, we evaluated the effects of UV-A exposure on J774 macrophage cells previously challenged with LPS in terms of oxidative distress, release of pro-inflammatory cytokines, and activation of regulated cell death pathways. Our results showed that LPS potentiates the dose-dependent UV-A-induced oxidative distress and cytokine release, in addition to amplifying the regulated (autophagy and apoptosis) and non-regulated (necrosis) mechanisms of cell death, indicating that a previous inflammatory stimulus potentiates UV-A-induced cell damage. We discuss these results in terms of the current-available skin care strategies.

Lactate metabolism in human health and disease

The current understanding of lactate extends from its origins as a byproduct of glycolysis to its role in tumor metabolism, as identified by studies on the Warburg effect. The lactate shuttle hypothesis suggests that lactate plays an important role as a bridging signaling molecule that coordinates signaling among different cells, organs and tissues. Lactylation is a posttranslational modification initially reported by Professor Yingming Zhao’s research group in 2019. Subsequent studies confirmed that lactylation is a vital component of lactate function and is involved in tumor proliferation, neural excitation, inflammation and other biological processes. An indispensable substance for various physiological cellular functions, lactate plays a regulatory role in different aspects of energy metabolism and signal transduction. Therefore, a comprehensive review and summary of lactate is presented to clarify the role of lactate in disease and to provide a reference and direction for future research. This review offers a systematic overview of lactate homeostasis and its roles in physiological and pathological processes, as well as a comprehensive overview of the effects of lactylation in various diseases, particularly inflammation and cancer.

Current Use of Fenton Reaction in Drugs and Food

Iron is the most abundant mineral in the human body and plays essential roles in sustaining life, such as the transport of oxygen to systemic organs. The Fenton reaction is the reaction between iron and hydrogen peroxide, generating hydroxyl radical, which is highly reactive and highly toxic to living cells. “Ferroptosis”, a programmed cell death in which the Fenton reaction is closely involved, has recently received much attention. Furthermore, various applications of the Fenton reaction have been reported in the medical and nutritional fields, such as cancer treatment or sterilization. Here, this review summarizes the recent growing interest in the usefulness of iron and its biological relevance through basic and practical information of the Fenton reaction and recent reports.

The Interplay between Autophagy and Redox Signaling in Cardiovascular Diseases

Reactive oxygen and nitrogen species produced at low levels under normal cellular metabolism act as important signal molecules. However, at increased production, they cause damage associated with oxidative stress, which can lead to the development of many diseases, such as cardiovascular, metabolic, neurodegenerative, diabetes, and cancer. The defense systems used to maintain normal redox homeostasis plays an important role in cellular responses to oxidative stress. The key players here are Nrf2-regulated redox signaling and autophagy. A tight interface has been described between these two processes under stress conditions and their role in oxidative stress-induced diseases progression. In this review, we focus on the role of Nrf2 as a key player in redox regulation in cell response to oxidative stress. We also summarize the current knowledge about the autophagy regulation and the role of redox signaling in this process. In line with the focus of our review, we describe in more detail information about the interplay between Nrf2 and autophagy pathways in myocardium and the role of these processes in cardiovascular disease development.

The Passage of H2O2 from Chloroplasts to Their Associated Nucleus during Retrograde Signalling: Reflections on the Role of the Nuclear Envelope

The response of chloroplasts to adverse environmental cues, principally increases in light intensity, stimulates chloroplast-to-nucleus retrograde signalling, which leads to the induction of immediate protective responses and longer-term acclimation. Hydrogen peroxide (H2O2), generated during photosynthesis, is proposed to both initiate and transduce a retrograde signal in response to photoinhibitory light intensities. Signalling specificity achieved by chloroplast-sourced H2O2 for signal transduction may be dependent upon the oft-observed close association of a proportion of these organelles with the nucleus. In this review, we consider more precisely the nature of the close association between a chloroplast appressed to the nucleus and the requirement for H2O2 to cross both the double membranes of the chloroplast and nuclear envelopes. Of particular relevance is that the endoplasmic reticulum (ER) has close physical contact with chloroplasts and is contiguous with the nuclear envelope. Therefore, the perinuclear space, which transducing H2O2 molecules would have to cross, may have an oxidising environment the same as the ER lumen. Based on studies in animal cells, the ER lumen may be a significant source of H2O2 in plant cells arising from the oxidative folding of proteins. If this is the case, then there is potential for the ER lumen/perinuclear space to be an important location to modify chloroplast-to-nucleus H2O2 signal transduction and thereby introduce modulation of it by additional different environmental cues. These would include for example, heat stress and pathogen infection, which induce the unfolded protein response characterised by an increased H2O2 level in the ER lumen.

Oxygen, pH, Lactate, and Metabolism-How Old Knowledge and New Insights Might Be Combined for New Wound Treatment

Over time, we have come to recognize a very complex network of physiological changes enabling wound healing. An immunological process enables the body to distinguish damaged cells and begin a cleaning mechanism by separating damaged proteins and cells with matrix metalloproteinases, a complement reaction, and free radicals. A wide variety of cell functions help to rebuild new tissue, dependent on energy provision and oxygen supply. Like in an optimized “bio-reactor,” disturbance can lead to prolonged healing. One of the earliest investigated local factors is the pH of wounds, studied in close relation to the local perfusion, oxygen tension, and lactate concentration. Granulation tissue with the wrong pH can hinder fibroblast and keratinocyte division and proliferation, as well as skin graft takes. Methods for influencing the pH have been tested, such as occlusion and acidification by the topical application of acidic media. In most trials, this has not changed the wound’s pH to an acidic one, but it has reduced the strong alkalinity of deeper or chronic wounds. Energy provision is essential for all repair processes. New insights into the metabolism of cells have changed the definition of lactate from a waste product to an indispensable energy provider in normoxic and hypoxic conditions. Neovascularization depends on oxygen provision and lactate, signaling hypoxic conditions even under normoxic conditions. An appropriate pH is necessary for successful skin grafting; hypoxia can change the pH of wounds. This review describes the close interconnections between the local lactate levels, metabolism, healing mechanisms, and pH. Furthermore, it analyzes and evaluates the different possible ways to support metabolism, such as lactate enhancement and pH adjustment. The aim of wound treatment must be the optimization of all these components. Therefore, the role of lactate and its influence on wound healing in acute and chronic wounds will be assessed.

Using circular economy principles to recycle materials in guiding the design of a wet scrubber-reactor for indoor air disinfection from coronavirus and other pathogens

An arduous need exists to discover rapid solutions to avoid the accelerated spread of coronavirus especially through the indoor environments like offices, hospitals, and airports. One such measure could be to disinfect the air, especially in indoor environments. The goal of this work is to propose a novel design of a wet scrubber-reactor to deactivate airborne microbes using circular economy principles. Based on Fenton's reaction mechanism, the system proposed here will deactivate airborne microbes (bioaerosols) such as SARS-CoV-2. The proposed design relies on using a highly porous clay-glass open-cell structure as an easily reproducible and cheap material. The principle behind this technique is an in-situ decomposition of hydrogen peroxide into highly reactive oxygen species and free radicals. The high porosity of a tailored ceramic structure provides a high contact area between atomized oxygen, free radicals and supplied polluted air. The design is shown to comply with the needs of achieving sustainable development goals.

EVI1 induces autophagy to promote drug resistance via regulation of ATG7 expression in leukemia cells

Ecotropic viral integration site 1 (EVI1) is an oncogenic transcription factor, which is abnormally expressed in myeloid leukemia and other several solid cancers. It is associated with short survival as well as anticancer drug resistance. Autophagy is a protective mechanism that promotes cancer cell growth and survival under stressed conditions including clinical drug treatment. Here evidences are provided that EVI1 induces autophagy and mediated drug resistance in myeloid leukemia cells. Both knockdown using RNAi and pharmacological inhibition of autophagy significantly increase sensitivity to cytotoxic drug treatment in EVI1high cells. Mechanistic studies revealed that EVI1 regulated autophagy by directly binding to autophagy-related gene autophagy related 7 (ATG7) promoter and transcriptionally upregulating its expression. Notably, ATG7 expression was positively correlated with EVI1 in bone marrow mononuclear cells from myeloid leukemia patients. Acute myeloid leukemia patients with high level of EVI1 are associated with unfavorable overall survival, which was aggravated by simultaneous high expression of ATG7 in these patients. Furthermore, ChIP and firefly luciferase reporter assay identified an EVI1-binding site at 227 upstream promoter region of ATG7 which regulated its transcription. In addition, enforced expression of EVI1 also increased intracellular reactive oxygen species and ATG7 mRNA levels as well as autophagy activity, whereas the increase was attenuated after treatment with reactive oxygen species scavenger, suggesting the involvement of reactive oxygen species in EVI1-induced autophagy. These findings demonstrate that EVI protects myeloid leukemia cell from anticancer drug treatment by inducing autophagy through dual control of ATG7. These results might present a new therapeutic approach for improving treatment outcome in myelogenous leukemia with EVI1high.

Putative Role of Nuclear Factor-Kappa B But Not Hypoxia-Inducible Factor-1α in Hypoxia-Dependent Regulation of Oxidative Stress in Hematopoietic Stem and Progenitor Cells

Aims: Adaptation to low oxygen of hematopoietic stem cells (HSCs) in the bone marrow has been demonstrated to depend on the activation of hypoxia-inducible factor (HIF)-1α as well as the limited production of reactive oxygen species (ROS). In this study, we aimed at determining whether HIF-1α is involved in protecting HSCs from ROS. Results: Oxidative stress was induced by DL-buthionine-(S,R)-sulfoximine (BSO)-treatment, which increases the mitochondrial ROS level. Hypoxia rescued Lineage-Sca-1+c-kit+ (LSK) cells from BSO-induced apoptosis, whereas cells succumbed to apoptosis in normoxia. Apoptosis in normoxia was inhibited with the antioxidant N-acetyl-L-cysteine or by overexpression of anti-apoptotic BCL-2. Moreover, stabilized expression of oxygen-insensitive HIFs could not protect LSK cells from oxidative stress-induced apoptosis at normoxia, neither could short hairpin RNA to Hif-1α inhibit the protective effects by hypoxia in LSK cells. Likewise, BSO treatment of LSK cells from Hif-1α knockout mice did not suppress the effects seen in hypoxia. Microarray analysis identified the nuclear factor-kappa B (NF-κB) pathway as a pathway induced by hypoxia. By using NF-κB lentiviral construct and DNA-binding assay, we found increased NF-κB activity in cells cultured in hypoxia compared with normoxia. Using an inhibitor against NF-κB activation, we could confirm the involvement of NF-κB signaling as BSO-mediated cell death was significantly increased in hypoxia after adding the inhibitor. Innovation: HIF-1α is not involved in protecting HSCs and progenitors to elevated levels of ROS on glutathione depletion during hypoxic conditions. Conclusion: The study proposes a putative role of NF-κB signaling as a hypoxia-induced regulator in early hematopoietic cells.

Liver Zonation in Health and Disease: Hypoxia and Hypoxia-Inducible Transcription Factors as Concert Masters

The liver and its zonation contribute to whole body homeostasis. Acute and chronic, not always liver, diseases impair proper metabolic zonation. Various underlying pathways, such as β-catenin, hedgehog signaling, and the Hippo pathway, along with the physiologically occurring oxygen gradient, appear to be contributors. Interestingly, hypoxia and hypoxia-inducible transcription factors can orchestrate those pathways. In the current review, we connect novel findings of liver zonation in health and disease and provide a view about the dynamic interplay between these different pathways and cell-types to drive liver zonation and systemic homeostasis.

Therapeutic potential of natural compounds in inflammation and chronic venous insufficiency

The term varicose vein refers to the twisted and swollen vein visible under the skin surface which occurs most commonly in the leg. Epidemiological studies report a varying percentage of incidences from 2 to 56% in men and <1-60% in women. Venous insufficiency is most often caused by the damage to the valves and walls of the veins. The mechanism of varicose vein formation is complex. It is, however, based on hypotensive blood vessels, hypoxia, and other mechanisms associated with inflammation. This work describes mechanisms related to the formation and development of the varicose vein. It discusses risk factors, pathogenesis of chronic venous disease, markers of the epithelial and leukocyte activation, state of hypoxia and inflammation, reactive oxygen species (ROS) generation, and oxidative stress. Additionally, this paper describes substances of plant origin used in the treatment of venous insufficiency. It also considers the structure of the molecules, their properties, and their mechanisms of action, the structure-activity relationship and chemical properties of flavonoids and other substances. The flavonoids include quercetin derivatives, micronized purified flavonoid fraction (Daflon), natural pine bark extract (Pycnogenol), and others such as triterpene saponine, extracts from Ruscus aculeatus and Centella asiatica, Ginkgo biloba extract, coumarin dereivatives that are used in chronic venous insufficiency. Flavonoids are natural substances found in plants, including fruits, vegetables, flowers, and others. They are important to the circulatory system and critical to blood vessels and the blood flow. Additionally, they have antioxidant, antiinflammatory properties.

Singlet oxygen mediated iron-based Fenton-like catalysis under nanoconfinement

In the bulk phase, hydroxyl radical from the one-electron transfer and high-valent iron-oxo species from the O-atom transfer compete to be the reactive intermediates in the Fenton and related reactions. In the confined space at a nanoscale, however, the behavior of the Fenton reaction is elusive. Herein, we report an unprecedented singlet oxygen mediated Fenton’s reaction occurred inside carbon nanotube with inner diameter of ∼7 nm, showing exotic catalytic activities, unforeseen adsorption-dependent selectivity, and pH stability for the oxidation of organic compounds. Our results suggest the use of Fenton’s reaction in more scenarios than ever explored.

For several decades, the iron-based Fenton-like catalysis has been believed to be mediated by hydroxyl radicals or high-valent iron-oxo species, while only sporadic evidence supported the generation of singlet oxygen (¹O₂) in the Haber–Weiss cycle. Herein, we report an unprecedented singlet oxygen mediated Fenton-like process catalyzed by ∼2-nm Fe₂O₃ nanoparticles distributed inside multiwalled carbon nanotubes with inner diameter of ∼7 nm. Unlike the traditional Fenton-like processes, this delicately designed system was shown to selectively oxidize the organic dyes that could be adsorbed with oxidation rates linearly proportional to the adsorption affinity. It also exhibited remarkably higher degradation activity (22.5 times faster) toward a model pollutant methylene blue than its nonconfined analog. Strikingly, the unforeseen stability at pH value up to 9.0 greatly expands the use of Fenton-like catalysts in alkaline conditions. This work represents a fundamental breakthrough toward the design and understanding of the Fenton-like system under nanoconfinement, might cause implications in other fields, especially in biological systems.

Cancer cells change their glucose metabolism to overcome increased ROS: One step from cancer cell to cancer stem cell?

Cancer cells can adapt to low energy sources in the face of ATP depletion as well as to their high levels of ROS by altering their metabolism and energy production networks which might also have a role in determining cell fate and developing drug resistance. Cancer cells are generally characterized by increased glycolysis. This is while; cancer stem cells (CSCs) exhibit an enhanced pentose phosphate pathway (PPP) metabolism. Based on the current literature, we suggest that cancer cells when encountering ROS, first increase the glycolysis rate and then following the continuation of oxidative stress, the metabolic balance is skewed from glycolysis to PPP. Therefore, we hypothesize in this review that in cancer cells this metabolic deviation during persistent oxidative stress might be a sign of cancer cells' shift towards CSCs, an issue that might be pivotal in more effective targeting of cancer cells and CSCs.

Hypoxia and Reactive Oxygen Species as Modulators of Endoplasmic Reticulum and Golgi Homeostasis

SIGNIFICANCE

Eukaryotic cells execute various functions in subcellular compartments or organelles for which cellular redox homeostasis is of importance. Apart from mitochondria, hypoxia and stress-mediated formation of reactive oxygen species (ROS) were shown to modulate endoplasmic reticulum (ER) and Golgi apparatus (GA) functions. Recent Advances: Research during the last decade has improved our understanding of disulfide bond formation, protein glycosylation and secretion, as well as pH and redox homeostasis in the ER and GA. Thus, oxygen (O₂) itself, NADPH oxidase (NOX) formed ROS, and pH changes appear to be of importance and indicate the intricate balance of intercompartmental communication.

CRITICAL ISSUES

Although the interplay between hypoxia, ER stress, and Golgi function is evident, the existence of more than 20 protein disulfide isomerase family members and the relative mild phenotypes of, for example, endoplasmic reticulum oxidoreductin 1 (ERO1)- and NOX4-knockout mice clearly suggest the existence of redundant and alternative pathways, which remain largely elusive.

FUTURE DIRECTIONS

The identification of these pathways and the key players involved in intercompartmental communication needs suitable animal models, genome-wide association, as well as proteomic studies in humans. The results of those studies will be beneficial for the understanding of the etiology of diseases such as type 2 diabetes, Alzheimer's disease, and cancer, which are associated with ROS, protein aggregation, and glycosylation defects.

Cu2+ selective chelators relieve copper-induced oxidative stress in vivo

Copper ions are essential for biological function yet are severely detrimental when present in excess. At the molecular level, copper ions catalyze the production of hydroxyl radicals that can irreversibly alter essential bio-molecules. Hence, selective copper chelators that can remove excess copper ions and alleviate oxidative stress will help assuage copper-overload diseases. However, most currently available chelators are non-specific leading to multiple undesirable side-effects. The challenge is to build chelators that can bind to copper ions with high affinity but leave the levels of essential metal ions unaltered. Here we report the design and development of redox-state selective Cu ion chelators that have 108 times higher conditional stability constants toward Cu2+ compared to both Cu+ and other biologically relevant metal ions. This unique selectivity allows the specific removal of Cu2+ ions that would be available only under pathophysiological metal overload and oxidative stress conditions and provides access to effective removal of the aberrant redox-cycling Cu ion pool without affecting the essential non-redox cycling Cu+ labile pool. We have shown that the chelators provide distinct protection against copper-induced oxidative stress in vitro and in live cells via selective Cu2+ ion chelation. Notably, the chelators afford significant reduction in Cu-induced oxidative damage in Atp7a-/- Menkes disease model cells that have endogenously high levels of Cu ions. Finally, in vivo testing of our chelators in a live zebrafish larval model demonstrate their protective properties against copper-induced oxidative stress.

Clinical imaging of hypoxia: Current status and future directions

Tissue hypoxia is a key feature of many important causes of morbidity and mortality. In pathologies such as stroke, peripheral vascular disease and ischaemic heart disease, hypoxia is largely a consequence of low blood flow induced ischaemia, hence perfusion imaging is often used as a surrogate for hypoxia to guide clinical diagnosis and treatment. Importantly, ischaemia and hypoxia are not synonymous conditions as it is not universally true that well perfused tissues are normoxic or that poorly perfused tissues are hypoxic. In pathologies such as cancer, for instance, perfusion imaging and oxygen concentration are less well correlated, and oxygen concentration is independently correlated to radiotherapy response and overall treatment outcomes. In addition, the progression of many diseases is intricately related to maladaptive responses to the hypoxia itself. Thus there is potentially great clinical and scientific utility in direct measurements of tissue oxygenation. Despite this, imaging assessment of hypoxia in patients is rarely performed in clinical settings. This review summarises some of the current methods used to clinically evaluate hypoxia, the barriers to the routine use of these methods and the newer agents and techniques being explored for the assessment of hypoxia in pathological processes.

Redox crosstalk at endoplasmic reticulum (ER) membrane contact sites (MCS) uses toxic waste to deliver messages

Many cellular redox reactions housed within mitochondria, peroxisomes and the endoplasmic reticulum (ER) generate hydrogen peroxide (H₂O₂) and other reactive oxygen species (ROS). The contribution of each organelle to the total cellular ROS production is considerable, but varies between cell types and also over time. Redox-regulatory enzymes are thought to assemble at a “redox triangle” formed by mitochondria, peroxisomes and the ER, assembling “redoxosomes” that sense ROS accumulations and redox imbalances. The redoxosome enzymes use ROS, potentially toxic by-products made by some redoxosome members themselves, to transmit inter-compartmental signals via chemical modifications of downstream proteins and lipids. Interestingly, important components of the redoxosome are ER chaperones and oxidoreductases, identifying ER oxidative protein folding as a key ROS producer and controller of the tri-organellar membrane contact sites (MCS) formed at the redox triangle. At these MCS, ROS accumulations could directly facilitate inter-organellar signal transmission, using ROS transporters. In addition, ROS influence the flux of Ca²⁺ ions, since many Ca²⁺ handling proteins, including inositol 1,4,5 trisphosphate receptors (IP₃Rs), SERCA pumps or regulators of the mitochondrial Ca²⁺ uniporter (MCU) are redox-sensitive. Fine-tuning of these redox and ion signaling pathways might be difficult in older organisms, suggesting a dysfunctional redox triangle may accompany the aging process.

Measurement of Reactive Oxygen Species, Reactive Nitrogen Species, and Redox-Dependent Signaling in the Cardiovascular System: A Scientific Statement From the American Heart Association

Reactive oxygen species and reactive nitrogen species are biological molecules that play important roles in cardiovascular physiology and contribute to disease initiation, progression, and severity. Because of their ephemeral nature and rapid reactivity, these species are difficult to measure directly with high accuracy and precision. In this statement, we review current methods for measuring these species and the secondary products they generate and suggest approaches for measuring redox status, oxidative stress, and the production of individual reactive oxygen and nitrogen species. We discuss the strengths and limitations of different methods and the relative specificity and suitability of these methods for measuring the concentrations of reactive oxygen and reactive nitrogen species in cells, tissues, and biological fluids. We provide specific guidelines, through expert opinion, for choosing reliable and reproducible assays for different experimental and clinical situations. These guidelines are intended to help investigators and clinical researchers avoid experimental error and ensure high-quality measurements of these important biological species.

Essential Roles of TIM-1 and TIM-4 Homologs in Adaptive Humoral Immunity in a Zebrafish Model

TIM-1 and TIM-4 proteins have become increasingly attractive for their critical functions in immune modulation, particularly in CD4(+) Th2 cell activation. Thus, these proteins were hypothesized to regulate adaptive humoral immunity. However, further evidence is needed to validate this hypothesis. This study describes the molecular and functional characteristics of TIM-1 and TIM-4 homologs from a zebrafish (Danio rerio) model (D. rerio TIM [DrTIM]-1 and DrTIM-4). DrTIM-1 and DrTIM-4 were predominantly expressed in CD4(+) T cells and MHC class II(+) APCs under the induction of Ag stimulation. Blockade or knockdown of both DrTIM-1 and DrTIM-4 significantly decreased Ag-specific CD4(+) T cell activation, B cell proliferation, Ab production, and vaccinated immunoprotection against bacterial infection. This result suggests that DrTIM-1 and DrTIM-4 serve as costimulatory molecules required for the full activation of adaptive humoral immunity. DrTIM-1 was detected to be a trafficking protein located in the cytoplasm of CD4(+) T cells. It can translocate onto the cell surface under stimulation by TIM-4-expressing APCs, which might be a precise regulatory strategy for CD4(+) T cells to avoid self-activation before APCs stimulation. Furthermore, a unique alternatively spliced soluble DrTIM-4 variant was identified to exert a negative regulatory effect on the proliferation of CD4(+) T cells. The above findings highlight a novel costimulatory mechanism underlying adaptive immunity. This study enriches the current knowledge on TIM-mediated immunity and provides a cross-species understanding of the evolutionary history of costimulatory systems throughout vertebrate evolution.

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy

Combining the concept of magnetic drug targeting and photodynamic therapy is a promising approach for the treatment of cancer. A high selectivity as well as significant fewer side effects can be achieved by this method, since the therapeutic treatment only takes place in the area where accumulation of the particles by an external electromagnet and radiation by a laser system overlap. In this article, a novel hypericin-bearing drug delivery system has been developed by synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) with a hypericin-linked functionalized dextran coating. For that, sterically stabilized dextran-coated SPIONs were produced by coprecipitation and crosslinking with epichlorohydrin to enhance stability. Carboxymethylation of the dextran shell provided a functionalized platform for linking hypericin via glutaraldehyde. Particle sizes obtained by dynamic light scattering were in a range of 55-85 nm, whereas investigation of single magnetite or maghemite particle diameter was performed by transmission electron microscopy and X-ray diffraction and resulted in approximately 4.5-5.0 nm. Surface chemistry of those particles was evaluated by Fourier transform infrared spectroscopy and ζ potential measurements, indicating successful functionalization and dispersal stabilization due to a mixture of steric and electrostatic repulsion. Flow cytometry revealed no toxicity of pure nanoparticles as well as hypericin without exposure to light on Jurkat T-cells, whereas the combination of hypericin, alone or loaded on particles, with light-induced cell death in a concentration and exposure time-dependent manner due to the generation of reactive oxygen species. In conclusion, the combination of SPIONs' targeting abilities with hypericin's phototoxic properties represents a promising approach for merging magnetic drug targeting with photodynamic therapy for the treatment of cancer.

Ferritin heavy chain mediates the protective effect of heme oxygenase-1 against oxidative stress

The phenomenon that heme oxygenase-1 (HO-1) protects cell from injury yet its enzymatic product, iron, may facilitate generation of free radical has been long puzzling. Here we establish a functional connection between ferritin heavy chain (FHC) and HO-1. In human lupus nephritis HO-1 and FHC are colocalized within the glomeruli. In rodent anti-Thy1 (thymocyte antigen 1) induced glomerulonephritis, heme oxygenase blockade lowers the expression of FHC and accelerates mesangial cell death. Stimulation of heme oxygenase in cultured rat mesangial cell enhances its resistance to hydrogen peroxide, whereas FHC knockdown by RNA interference compromises this salutary effect. RNA interference of HO-1 makes the cell more susceptible to hydrogen peroxide, which can be rescued by forced expression of wild-type FHC but not mutants that lose the capacity of iron storage and ferroxidase activity. Phosphorylation of JunD was not sustained in these cells. Microarray analysis identifies four candidate transcriptional factors that may regulate the HO-1-induced transcription of FHC. Our results support the role of FHC in neutralizing the iron toxicity as well as mediating the protective effect of HO-1 in response to oxidative stress.

Golgi Associated HIF1a Serves as a Reserve in Melanoma Cells

Hypoxia-inducible factor-1alpha (HIF1a) is a key transcriptional regulator that enables cellular metabolic adaptation to low levels of oxygen. Multiple mechanisms, including lysosomal degradation, control the levels of HIF1a protein. Here we show that HIF1a protein degradation is resistant to lysosomal inhibition and that HIF1a is associated with the Golgi compartment in melanoma cells. Although pharmacological inhibitors of prolyl hydroxylation, neddylation and the proteasome inhibited degradation of HIF1a, attenuation of lysosomal activity with chloroquine did not alter the levels of HIF1a or its association with Golgi. Pharmacological disruption of Golgi resulted in nuclear accumulation of HIF1a. However, blockade of ER-Golgi protein transport in hypoxia reduced the transcript levels of HIF1a target genes. These findings suggest a possible role for the oxygen-dependent protein folding process from the ER-Golgi compartment in fine-tuning HIF1a transcriptional output.

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

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Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

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Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

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NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

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ROS are powerful post-transcriptional and epigenetic regulators.

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Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Antioxidant responses and cellular adjustments to oxidative stress

Redox biological reactions are now accepted to bear the Janus faceted feature of promoting both physiological signaling responses and pathophysiological cues. Endogenous antioxidant molecules participate in both scenarios. This review focuses on the role of crucial cellular nucleophiles, such as glutathione, and their capacity to interact with oxidants and to establish networks with other critical enzymes such as peroxiredoxins. We discuss the importance of the Nrf2-Keap1 pathway as an example of a transcriptional antioxidant response and we summarize transcriptional routes related to redox activation. As examples of pathophysiological cellular and tissular settings where antioxidant responses are major players we highlight endoplasmic reticulum stress and ischemia reperfusion. Topologically confined redox-mediated post-translational modifications of thiols are considered important molecular mechanisms mediating many antioxidant responses, whereas redox-sensitive microRNAs have emerged as key players in the posttranscriptional regulation of redox-mediated gene expression. Understanding such mechanisms may provide the basis for antioxidant-based therapeutic interventions in redox-related diseases.

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Antioxidant responses are crucial for both redox signaling and redox damage.

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Glutathione-mediated reactions and Nrf2-Keap1 pathway are key antioxidant responses.

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Redox-related post-translational modifications activate specific signaling pathways.

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Redox-sensitive microRNAs contribute to redox-mediated gene expression regulation.

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ER stress and ischemia-reperfusion are antioxidant-related pathophysiological events.

The control of reactive oxygen species production by SHP-1 in oligodendrocytes

We have previously described reduced myelination and corresponding myelin basic protein (MBP) expression in the central nervous system of Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) deficient motheaten (me/me) mice compared with normal littermate controls. Deficiency in myelin and MBP expression in both brains and spinal cords of motheaten mice correlated with reduced MBP mRNA expression levels in vivo and in purified oligodendrocytes in vitro. Therefore, SHP-1 activity seems to be a critical regulator of oligodendrocyte gene expression and function. Consistent with this role, this study demonstrates that oligodendrocytes of motheaten mice and SHP-1-depleted N20.1 cells produce higher levels of reactive oxygen species (ROS) and exhibit corresponding markers of increased oxidative stress. In agreement with these findings, we demonstrate that increased production of ROS coincides with ROS-induced signaling pathways known to affect myelin gene expression in oligodendrocytes. Antioxidant treatment of SHP-1-deficient oligodendrocytes reversed the pathological changes in these cells, with increased myelin protein gene expression and decreased expression of nuclear factor (erythroid-2)-related factor 2 (Nrf2) responsive gene, heme oxygenase-1 (HO-1). Furthermore, we demonstrate that SHP-1 is expressed in human white matter oligodendrocytes, and there is a subset of multiple sclerosis subjects that demonstrate a deficiency of SHP-1 in normal-appearing white matter. These studies reveal critical pathways controlled by SHP-1 in oligodendrocytes that relate to susceptibility of SHP-1-deficient mice to both developmental defects in myelination and to inflammatory demyelinating diseases.

Endoplasmic reticulum chaperones and oxidoreductases: critical regulators of tumor cell survival and immunorecognition

Endoplasmic reticulum (ER) chaperones and oxidoreductases are abundant enzymes that mediate the production of fully folded secretory and transmembrane proteins. Resisting the Golgi and plasma membrane-directed “bulk flow,” ER chaperones and oxidoreductases enter retrograde trafficking whenever they are pulled outside of the ER by their substrates. Solid tumors are characterized by the increased production of reactive oxygen species (ROS), combined with reduced blood flow that leads to low oxygen supply and ER stress. Under these conditions, hypoxia and the unfolded protein response upregulate their target genes. When this occurs, ER oxidoreductases and chaperones become important regulators of tumor growth. However, under these conditions, these proteins not only promote the folding of proteins, but also alter the properties of the plasma membrane and hence modulate tumor immune recognition. For instance, high levels of calreticulin serve as an “eat-me” signal on the surface of tumor cells. Conversely, both intracellular and surface BiP/GRP78 promotes tumor growth. Other ER folding assistants able to modulate the properties of tumor tissue include protein disulfide isomerase (PDI), Ero1α and GRP94. Understanding the roles and mechanisms of ER chaperones in regulating tumor cell functions and immunorecognition will lead to important insight for the development of novel cancer therapies.

Targeting tumour hypoxia to prevent cancer metastasis. From biology, biosensing and technology to drug development: the METOXIA consortium

The hypoxic areas of solid cancers represent a negative prognostic factor irrespective of which treatment modality is chosen for the patient. Still, after almost 80 years of focus on the problems created by hypoxia in solid tumours, we still largely lack methods to deal efficiently with these treatment-resistant cells. The consequences of this lack may be serious for many patients: Not only is there a negative correlation between the hypoxic fraction in tumours and the outcome of radiotherapy as well as many types of chemotherapy, a correlation has been shown between the hypoxic fraction in tumours and cancer metastasis. Thus, on a fundamental basis the great variety of problems related to hypoxia in cancer treatment has to do with the broad range of functions oxygen (and lack of oxygen) have in cells and tissues. Therefore, activation-deactivation of oxygen-regulated cascades related to metabolism or external signalling are important areas for the identification of mechanisms as potential targets for hypoxia-specific treatment. Also the chemistry related to reactive oxygen radicals (ROS) and the biological handling of ROS are part of the problem complex. The problem is further complicated by the great variety in oxygen concentrations found in tissues. For tumour hypoxia to be used as a marker for individualisation of treatment there is a need for non-invasive methods to measure oxygen routinely in patient tumours. A large-scale collaborative EU-financed project 2009-2014 denoted METOXIA has studied all the mentioned aspects of hypoxia with the aim of selecting potential targets for new hypoxia-specific therapy and develop the first stage of tests for this therapy. A new non-invasive PET-imaging method based on the 2-nitroimidazole [(18)F]-HX4 was found to be promising in a clinical trial on NSCLC patients. New preclinical models for testing of the metastatic potential of cells were developed, both in vitro (2D as well as 3D models) and in mice (orthotopic grafting). Low density quantitative real-time polymerase chain reaction (qPCR)-based assays were developed measuring multiple hypoxia-responsive markers in parallel to identify tumour hypoxia-related patterns of gene expression. As possible targets for new therapy two main regulatory cascades were prioritised: The hypoxia-inducible-factor (HIF)-regulated cascades operating at moderate to weak hypoxia (<1% O(2)), and the unfolded protein response (UPR) activated by endoplasmatic reticulum (ER) stress and operating at more severe hypoxia (<0.2%). The prioritised targets were the HIF-regulated proteins carbonic anhydrase IX (CAIX), the lactate transporter MCT4 and the PERK/eIF2α/ATF4-arm of the UPR. The METOXIA project has developed patented compounds targeting CAIX with a preclinical documented effect. Since hypoxia-specific treatments alone are not curative they will have to be combined with traditional anti-cancer therapy to eradicate the aerobic cancer cell population as well.

GSK3β-dependent phosphorylation alters DNA binding, transactivity and half-life of the transcription factor USF2

The upstream stimulatory factor 2 (USF2) is a regulator of important cellular processes and is supposed to have also a role during tumor development. However, the knowledge about the mechanisms that control the function of USF2 is limited. The data of the current study show that USF2 function is regulated by phosphorylation and identified GSK3β as an USF2-phosphorylating kinase. The phosphorylation sites within USF2 could be mapped to serine 155 and threonine 230. In silico analyses of the 3-dimensional structure revealed that phosphorylation of USF2 by GSK3β converts it to a more open conformation which may influence transactivity, DNA binding and target gene expression. Indeed, experiments with GSK-3β-deficient cells revealed that USF2 transactivity, DNA binding and target gene expression were reduced upon lack of GSK3β. Further, experiments with USF2 variants mimicking GSK3β phosphorylated USF2 in GSK3β-deficient cells showed that phosphorylation of USF2 by GSK3β did not affect cell proliferation but increased cell migration. Together, this study reports a new mechanism by which USF2 may contribute to cancerogenesis.

Bilirubin activates transcription of HIF-1α in human proximal tubular cells cultured in the physiologic oxygen content

The expression of hypoxia-inducible factor (HIF) is influenced by reactive oxygen species (ROS). Effect of bilirubin on HIF-1 expression in proximal tubular cells was investigated under physiological oxygen concentration, which is relative hypoxic condition mimicking oxygen content in the medulla of renal tissue. The human kidney (HK2) cells were cultured in 5% oxygen with or without bilirubin. HIF-1α protein expression was increased by bilirubin treatment at 0.01-0.2 mg/dL concentration. The messenger RNA expression of HIF-1α was increased by 1.69±0.05 folds in the cells cultured with 0.1 mg/dL bilirubin, compared to the control cells. The inhibitors of PI3K/mTOR, PI3K/AKT, and ERK 1/2 pathways did not attenuate increased HIF-1α expression by bilirubin. HIF-1α expression decreased by 10 µM exogenous hydrogen peroxide (H2O2); scavenger of ROS with or without bilirubin in the HK2 cells increased HIF-1α concentration more than that in the cells without bilirubin. Exogenous H2O2 decreased the phosphorylation of P70S6 kinase, which was completely reversed by bilirubin treatment. Knockdown of NOX4 gene by small interfering RNA (siRNA) increased HIF-1α mRNA expression. In coonclusion, bilirubin enhances HIF-1α transcription as well as the up-regulation of HIF-1α protein translation through the attenuation of ROS and subunits of NADPH oxidase.

Exploiting oxidative microenvironments in the body as triggers for drug delivery systems

SIGNIFICANCE

Reactive oxygen species and reactive nitrogen species (ROS/RNS) play an important role in cell signaling pathways. However, the increased production of these species may disrupt cellular homeostasis, giving rise to pathological conditions. Biomaterials that are responsive to ROS/RNS can be strategically used to specifically release therapeutics and diagnostic agents to regions undergoing oxidative stress.

RECENT ADVANCES

Many nanocarriers intended to exploit redox micro-environments as triggers for drug release, summarized and compared in this review, have recently been developed. We describe these carriers' chemical structures, strategies for payload protection and oxidation-selective release, and ROS/RNS sensitivity as tested in initial studies.

CRITICAL ISSUES

ROS/RNS are unstable, so reliable measures of their concentrations in various conditions are scarce. Combined with the dearth of materials shown to respond to physiologically relevant levels of ROS/RNS, evaluations of their true sensitivity are difficult.

FUTURE DIRECTIONS

Oxidation-responsive nanocarriers developed thus far show tremendous potential for applicability in vivo; however, the sensitivity of these chemistries needs to be fine tuned to enable responses to physiological levels of ROS and RNS.

Oxidative stress, redox signaling, and autophagy: cell death versus survival

SIGNIFICANCE

The molecular machinery regulating autophagy has started becoming elucidated, and a number of studies have undertaken the task to determine the role of autophagy in cell fate determination within the context of human disease progression. Oxidative stress and redox signaling are also largely involved in the etiology of human diseases, where both survival and cell death signaling cascades have been reported to be modulated by reactive oxygen species (ROS) and reactive nitrogen species (RNS).

RECENT ADVANCES

To date, there is a good understanding of the signaling events regulating autophagy, as well as the signaling processes by which alterations in redox homeostasis are transduced to the activation/regulation of signaling cascades. However, very little is known about the molecular events linking them to the regulation of autophagy. This lack of information has hampered the understanding of the role of oxidative stress and autophagy in human disease progression.

CRITICAL ISSUES

In this review, we will focus on (i) the molecular mechanism by which ROS/RNS generation, redox signaling, and/or oxidative stress/damage alter autophagic flux rates; (ii) the role of autophagy as a cell death process or survival mechanism in response to oxidative stress; and (iii) alternative mechanisms by which autophagy-related signaling regulate mitochondrial function and antioxidant response.

FUTURE DIRECTIONS

Our research efforts should now focus on understanding the molecular basis of events by which autophagy is fine tuned by oxidation/reduction events. This knowledge will enable us to understand the mechanisms by which oxidative stress and autophagy regulate human diseases such as cancer and neurodegenerative disorders.

Ischemia induces different levels of hypoxia inducible factor-1α protein expression in interneurons and pyramidal neurons

Introduction

Pyramidal (glutamatergic) neurons and interneurons are morphologically and functionally well defined in the central nervous system. Although it is known that glutamatergic neurons undergo immediate cell death whereas interneurons are insensitive or survive longer during cerebral ischemia, the protection mechanisms responsible for this interneuronal survival are not well understood. Hypoxia inducible factor-1 (HIF-1) plays an important role in protecting neurons from hypoxic/ischemic insults. Here, we studied the expression of HIF-1α, the regulatable subunit of HIF-1, in the different neuronal phenotypes under in vitro and in vivo ischemia.

Results

In a primary cortical culture, HIF-1α expression was observed in neuronal somata after hypoxia (1% oxygen) in the presence of 5 or 25 mM glucose but not under normoxia (21% oxygen). Interestingly, only certain MAP2-positive neurons containing round somata (interneuron-like morphology) co-localized with HIF-1α staining. Other neurons such as pyramidal-like neurons showed no expression of HIF-1α under either normoxia or hypoxia. The HIF-1α positive neurons were GAD65/67 positive, confirming that they were interneuron-type cells. The HIF-1α expressing GAD65/67-positive neurons also possessed high levels of glutathione. We further demonstrated that ischemia induced significant HIF-1α expression in interneurons but not in pyramidal neurons in a rat model of middle cerebral artery occlusion.

Conclusion

These results suggest that HIF-1α protein expression induced by ischemia is neuron-type specific and that this specificity may be related to the intracellular level of glutathione (GSH).

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Neurodegeneration in multiple sclerosis involves multiple pathogenic mechanisms

Multiple sclerosis (MS) is a complex autoimmune disease that impairs the central nervous system (CNS). The neurological disability and clinical course of the disease is highly variable and unpredictable from one patient to another. The cause of MS is still unknown, but it is thought to occur in genetically susceptible individuals who develop disease due to a nongenetic trigger, such as altered metabolism, a virus, or other environmental factors. MS patients develop progressive, irreversible, neurological disability associated with neuronal and axonal damage, collectively known as neurodegeneration. Neurodegeneration was traditionally considered as a secondary phenomenon to inflammation and demyelination. However, recent data indicate that neurodegeneration develops along with inflammation and demyelination. Thus, MS is increasingly recognized as a neurodegenerative disease triggered by an inflammatory attack of the CNS. While both inflammation and demyelination are well described and understood cellular processes, neurodegeneration might be defined by a diverse pool of any of the following: neuronal cell death, apoptosis, necrosis, and virtual hypoxia. In this review, we present multiple theories and supporting evidence that identify common biological processes that contribute to neurodegeneration in MS.

Magnetite- and maghemite-induced different toxicity in murine alveolar macrophage cells

The unique properties of nanoparticles and biological systems are important factors affecting the biological response following nanoparticle exposure. Iron oxide nanoparticles are classified mainly as magnetite (M-FeNPs) and maghemite (NM-FeNPs). In our previous study, NM-FeNPs induced autophagic cell death in RAW264.7, a murine peritoneal macrophage cell line, which has excellent lysosomal activity. In this study, we compared the toxicity of M-FeNPs and NM-FeNPs in MH-S, a murine alveolar macrophage cell line, which has relatively low lysosomal activity. At 24 h post-exposure, M-FeNPs decreased cell viability and ATP production, and elevated the levels of reactive oxygen species, nitric oxide, and pro-inflammatory cytokines to a higher extent than NM-FeNPs. Damage of mitochondria and the endoplasmic reticulum and the down-regulation of mitochondrial function and transcription-related genes were also higher in cells exposed to M-FeNPs than in cells exposed to NM-FeNPs (50 μg/ml). In addition, cells exposed to M-FeNPs (50 μg/ml) showed an increase in the number of autophagosome-like vacuoles, whereas cells exposed to NM-FeNPs formed large vacuoles in the cytosol. However, an autophagy-related molecular response was not induced by exposure to either FeNPs, unlike the results seen in our previous study with RAW264.7 cells. We suggest that M-FeNPs induced higher toxicity compared to NM-FeNPs in MH-S cells, and lysosomal activity plays an important role in determining cell death pathway.

Sensing hypoxia by mitochondria: a unifying hypothesis involving S-nitrosation

SIGNIFICANCE

Sudden hypoxia requires a rapid response in tissues with high energy demand. Mitochondria are rapid sensors for a lack of oxygen, but no consistent mechanism for the sensing process and the subsequent counter-regulation has been described.

RECENT ADVANCES

In the present hypothesis review, we suggest an oxygen-sensing mechanism by mitochondria that is initiated at low oxygen tension by electrons from the respiratory chain, leading to the reduction of intracellular nitrite to nitric oxide ((•)NO) that would subsequently compete with oxygen for binding to cytochrome c oxidase. This allows superoxide ((•)O2(-)) formation in hypoxic areas, leading to S-nitrosation and the inhibition of mitochondrial Krebs cycle enzymes. With more formation of (•)O2(-), peroxynitrite is generated and known to damage the connection between the mitochondrial matrix and the outer membrane.

CRITICAL ISSUES

A fundamental question on a regulatory mechanism is its reversibility. Readmission of oxygen and opening of the mitochondrial KATP-channel would allow electrons from glycerol-3-phosphate to selectively reduce the ubiquinone pool to generate (•)O2(-) at both sides of the inner mitochondrial membrane. On the cytosolic side, superoxide is dismutated and will support H2O2/Fe(2+)-dependent transcription processes and on the mitochondrial matrix side, it could lead to the one-electron reduction and reactivation of S-nitrosated proteins.

FUTURE DIRECTIONS

It remains to be elucidated up to which stage the herein proposed silencing of mitochondria remains reversible and when irreversible changes that ultimately lead to classical reperfusion injury are initiated.

Nutritional countermeasures targeting reactive oxygen species in cancer: from mechanisms to biomarkers and clinical evidence

Reactive oxygen species (ROS) exert various biological effects and contribute to signaling events during physiological and pathological processes. Enhanced levels of ROS are highly associated with different tumors, a Western lifestyle, and a nutritional regime. The supplementation of food with traditional antioxidants was shown to be protective against cancer in a number of studies both in vitro and in vivo. However, recent large-scale human trials in well-nourished populations did not confirm the beneficial role of antioxidants in cancer, whereas there is a well-established connection between longevity of several human populations and increased amount of antioxidants in their diets. Although our knowledge about ROS generators, ROS scavengers, and ROS signaling has improved, the knowledge about the direct link between nutrition, ROS levels, and cancer is limited. These limitations are partly due to lack of standardized reliable ROS measurement methods, easily usable biomarkers, knowledge of ROS action in cellular compartments, and individual genetic predispositions. The current review summarizes ROS formation due to nutrition with respect to macronutrients and antioxidant micronutrients in the context of cancer and discusses signaling mechanisms, used biomarkers, and its limitations along with large-scale human trials.

Reactive oxygen species and the cardiovascular system

Ever since the discovery of free radicals, many hypotheses on the deleterious actions of reactive oxygen species (ROS) have been proposed. However, increasing evidence advocates the necessity of ROS for cellular homeostasis. ROS are generated as inherent by-products of aerobic metabolism and are tightly controlled by antioxidants. Conversely, when produced in excess or when antioxidants are depleted, ROS can inflict damage to lipids, proteins, and DNA. Such a state of oxidative stress is associated with many pathological conditions and closely correlated to oxygen consumption. Although the deleterious effects of ROS can potentially be reduced by restoring the imbalance between production and clearance of ROS through administration of antioxidants (AOs), the dosage and type of AOs should be tailored to the location and nature of oxidative stress. This paper describes several pathways of ROS signaling in cellular homeostasis. Further, we review the function of ROS in cardiovascular pathology and the effects of AOs on cardiovascular outcomes with emphasis on the so-called oxidative paradox.

Autophagy and ageing: insights from invertebrate model organisms

Ageing in diverse species ranging from yeast to humans is associated with the gradual, lifelong accumulation of molecular and cellular damage. Autophagy, a conserved lysosomal, self-destructive process involved in protein and organelle degradation, plays an essential role in both cellular and whole-animal homeostasis. Accumulating evidence now indicates that autophagic degradation declines with age and this gradual reduction of autophagy might have a causative role in the functional deterioration of biological systems during ageing. Indeed, loss of autophagy gene function significantly influences longevity. Moreover, genetic or pharmacological manipulations that extend lifespan in model organisms often activate autophagy. Interestingly, conserved signalling pathways and environmental factors that regulate ageing, such as the insulin/IGF-1 signalling pathway and oxidative stress response pathways converge on autophagy. In this article, we survey recent findings in invertebrates that contribute to advance our understanding of the molecular links between autophagy and the regulation of ageing. In addition, we consider related mechanisms in other organisms and discuss their similarities and idiosyncratic features in a comparative manner.

Hypoxia-inducible factor 1 protects hypoxic astrocytes against glutamate toxicity

Stroke is a major neurological disorder characterized by an increase in the Glu (glutamate) concentration resulting in excitotoxicity and eventually cellular damage and death in the brain. HIF-1 (hypoxia-inducible factor-1), a transcription factor, plays an important protective role in promoting cellular adaptation to hypoxic conditions. It is known that HIF-1α, the regulatable subunit of HIF-1, is expressed by astrocytes under severe ischaemia. However, the effect of HIF-1 on astrocytes following Glu toxicity during ischaemia has not been well studied. We investigated the role of HIF-1 in protecting ischaemic astrocytes against Glu toxicity. Immunostaining with GFAP (glial fibrillary acidic protein) confirmed the morphological modification of astrocytes in the presence of 1 mM Glu under normoxia. Interestingly, when the astrocytes were exposed to severe hypoxia (0.1% O₂), the altered cell morphology was ameliorated with up-regulation of HIF-1α. To ascertain HIF-1's protective role, effects of two HIF-1α inhibitors, YC-1 [3-(50-hydroxymethyl-20-furyl)-1-benzylindazole] and 2Me2 (2-methoxyoestradiol), were tested. Both the inhibitors decreased the recovery in astrocyte morphology and increased cell death. Given that ischaemia increases ROS (reactive oxygen species), we examined the role of GSH (reduced glutathione) in the mechanism for this protection. GSH was increased under hypoxia, and this correlated with an increase in HIF-1α stabilization in the astrocytes. Furthermore, inhibition of GSH with BSO (l-butathione sulfoximine) decreased HIF-1α expression, suggesting its role in the stabilization of HIF-1α. Overall, our results indicate that the expression of HIF-1α under hypoxia has a protective effect on astrocytes in maintaining cell morphology and viability in response to Glu toxicity.

Low-molecular-weight oxidants involved in disulfide bond formation

SIGNIFICANCE

The biogenesis of most secreted and outer membrane proteins involves the formation of structure stabilizing disulfide bonds. Hence knowledge of the mechanisms for their formation is critical for understanding a myriad of cellular processes and associated disease states.

RECENT ADVANCES

Until recently it was thought that members of the Ero1 sulfhydryl oxidase family were responsible for catalyzing the majority of disulfide bond formation in the endoplasmic reticulum. However, multiple eukaryotic organisms are now known to show no or minor phenotypes when these enzymatic pathways are disrupted, suggesting that other pathways can catalyze disulfide bond formation to an extent sufficient to maintain normal physiology.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This lack of a strong phenotype raises multiple questions regarding what pathways are acting and whether they themselves constitute the major route for disulfide bond formation. This review critically examines the potential low molecular oxidants that maybe involved in the catalyzed or noncatalyzed formation of disulfide bonds, with an emphasis on the mammalian endoplasmic reticulum, via an examination of their thermodynamics, kinetics, and availability and gives pointers to help guide future experimental work.

Hypoxia inducible factor-1: its potential role in cerebral ischemia

A divergence in the supply and consumption of oxygen in brain tissue initiates complex cycle of biochemical and molecular events resulting in neuronal death. To overcome such adverse situation, the tissue has to adopt some cellular mechanisms such as induction of various transcription factors, such as hypoxia inducible factor (HIF). It is a transcriptional regulator of oxygen homeostasis and key factor to generate the adaptive responses through upregulation of various target genes involved in the erythropoiesis, angiogenesis as well as glucose metabolism and transport. On the other hand, some studies do suggest that HIF also plays a detrimental role in ischemic reperfusion injury by inducing the pro apoptotic molecules, cytokines such as Nix, BNip3, and IL-20 which cause mitochondrial dysfunction leading to cell death. Hence, modulation of HIF-1 activity seems to provide an innovative therapeutic target to reduce the cellular damage, which arises from ischemic injury. Apart from traditional oxygen dependent HIF regulation, the focus has now shifted toward oxygen independent regulation in cell specific manner through reactive oxygen species involving hypoxia-associated factor, and heat shock protein 90, etc. Therefore, future development of such small molecule regulators for HIF-1 stability and signaling may prove useful to therapeutically target for enhancing recovery and repair in I/R injury.