High rates of extracellular superoxide generation by cultured human fibroblasts: involvement of a lipid-metabolizing enzyme

Engineered stem cell-based strategy: A new paradigm of next-generation stem cell product in regenerative medicine

Stem cells have garnered significant attention in regenerative medicine owing to their abilities of multi-directional differentiation and self-renewal. Despite these encouraging results, the market for stem cell products yields limited, which is largely due to the challenges faced to the safety and viability of stem cells in vivo. Besides, the fate of cells re-infusion into the body unknown is also a major obstacle to stem cell therapy. Actually, both the functional protection and the fate tracking of stem cells are essential in tissue homeostasis, repair, and regeneration. Recent studies have utilized cell engineering techniques to modify stem cells for enhancing their treatment efficiency or imparting them with novel biological capabilities, in which advances demonstrate the immense potential of engineered cell therapy. In this review, we proposed that the "engineered stem cells" are expected to represent the next generation of stem cell therapies and reviewed recent progress in this area. We also discussed potential applications of engineered stem cells and highlighted the most common challenges that must be addressed. Overall, this review has important guiding significance for the future design of new paradigms of stem cell products to improve their therapeutic efficacy.

Biological autoluminescence as a perturbance-free method for monitoring oxidation in biosystems

Biological oxidation processes are in the core of life energetics, play an important role in cellular biophysics, physiological cell signaling or cellular pathophysiology. Understanding of biooxidation processes is also crucial for biotechnological applications. Therefore, a plethora of methods has been developed for monitoring oxidation so far, each with distinct advantages and disadvantages. We review here the available methods for monitoring oxidation and their basic characteristics and capabilities. Then we focus on a unique method - the only one that does not require input of additional external energy or chemicals - which employs detection of biological autoluminescence (BAL). We highlight the pros and cons of this method and provide an overview of how BAL can be used to report on various aspects of cellular oxidation processes starting from oxygen consumption to the generation of oxidation products such as carbonyls. This review highlights the application potential of this completely non-invasive and label-free biophotonic diagnostic method.

Regulation of pathophysiological and tissue regenerative functions of MSCs mediated via the WNT signaling pathway (Review)

Tissues have remarkable natural capabilities to regenerate for the purpose of physiological turnover and repair of damage. Adult mesenchymal stem cells (MSCs) are well known for their unique self-renewal ability, pluripotency, homing potential, paracrine effects and immunomodulation. Advanced research of the unique properties of MSCs have opened up new horizons for tissue regenerative therapies. However, certain drawbacks of the application of MSCs, such as the low survival rate of transplanted MSCs, unsatisfactory efficiency and even failure to regenerate under an unbalanced microenvironment, are concerning with regards to their wider therapeutic applications. The activity of stem cells is mainly regulated by the anatomical niche; where they are placed during their clinical and therapeutic applications. Crosstalk between various niche signals maintains MSCs in homeostasis, in which the WNT signaling pathway plays vital roles. Several external or internal stimuli have been reported to interrupt the normal bioactivity of stem cells. The irreversible tissue loss that occurs during infection at the site of tissue grafting suggests an inhibitory effect mediated by microbial infections within MSC niches. In addition, MSC-seeded tissue engineering success is difficult in various tissues, when sites of injury are under the effects of a severe infection despite the immunomodulatory properties of MSCs. In the present review, the current understanding of the way in which WNT signaling regulates MSC activity modification under physiological and pathological conditions was summarized. An effort was also made to illustrate parts of the underlying mechanism, including the inflammatory factors and their interactions with the regulatory WNT signaling pathway, aiming to promote the clinical translation of MSC-based therapy.

Photobiomodulation of mineralisation in mesenchymal stem cells

Mesenchymal stem cells (MSCs) and photobiomodulation (PBM) both offer significant therapeutic potential in regenerative medicine. MSCs have the ability to self-renew and differentiate; giving rise to multiple cellular and tissue lineages that are utilised in repair and regeneration of damaged tissues. PBM utilises light energy delivered at a range of wavelengths to promote wound healing. The positive effects of light on MSC proliferation are well documented; and recently, several studies have determined the outcomes of PBM on mineralised tissue differentiation in MSC populations. As PBM effects are biphasic, it is important to understand the underlying cellular regulatory mechanisms, as well as, provide accurate details of the irradiation conditions, to optimise and standardise outcomes. This review article focuses on the use of red, near-infra-red (R/NIR) and blue wavelengths to promote the mineralisation potential of MSCs; and also reports on the possible molecular mechanisms which underpin transduction of these effects. A variety of potential photon absorbers have been identified which are reported to mediate the signalling mechanisms, including respiratory chain enzymes, flavins, and cryptochromes. Studies report that R/NIR and blue light stimulate MSC differentiation by enhancing respiratory chain activity and increasing reactive oxygen species levels; however, currently, there are considerable variations between irradiation parameters reported. We conclude that due to its non-invasive properties, PBM may, following optimisation, provide an efficient therapeutic approach to clinically support MSC-mediated hard tissue repair. However, to optimise application, further studies are required to identify appropriate light delivery parameters, as well as elucidate the photo-signalling mechanisms involved.

Regulation of the mitochondrial reactive oxygen species: Strategies to control mesenchymal stem cell fates ex vivo and in vivo

Mesenchymal stem cells (MSCs) are broadly used in cell‐based regenerative medicine because of their self‐renewal and multilineage potencies in vitro and in vivo. To ensure sufficient amounts of MSCs for therapeutic purposes, cells are generally cultured in vitro for long‐term expansion or specific terminal differentiation until cell transplantation. Although physiologically up‐regulated reactive oxygen species (ROS) production is essential for maintenance of stem cell activities, abnormally high levels of ROS can harm MSCs both in vitro and in vivo. Overall, additional elucidation of the mechanisms by which physiological and pathological ROS are generated is necessary to better direct MSC fates and improve their therapeutic effects by controlling external ROS levels. In this review, we focus on the currently revealed ROS generation mechanisms and the regulatory routes for controlling their rates of proliferation, survival, senescence, apoptosis, and differentiation. A promising strategy in future regenerative medicine involves regulating ROS generation via various means to augment the therapeutic efficacy of MSCs, thus improving the prognosis of patients with terminal diseases.

Regulation of neuronal development and function by ROS

Reactive oxygen species (ROS) have long been studied as destructive agents in the context of nervous system ageing, disease and degeneration. Their roles as signalling molecules under normal physiological conditions is less well understood. Recent studies have provided ample evidence of ROS-regulating neuronal development and function, from the establishment of neuronal polarity to growth cone pathfinding; from the regulation of connectivity and synaptic transmission to the tuning of neuronal networks. Appreciation of the varied processes that are subject to regulation by ROS might help us understand how changes in ROS metabolism and buffering could progressively impact on neuronal networks with age and disease.

Chemical composition and phagocyte immunomodulatory activity of Ferula iliensis essential oils

Essential oil extracts from Ferula iliensis have been used traditionally in Kazakhstan for treatment of inflammation and other illnesses. Because little is known about the biologic activity of these essential oils that contributes to their therapeutic properties, we analyzed their chemical composition and evaluated their phagocyte immunomodulatory activity. The main components of the extracted essential oils were (E)-propenyl sec-butyl disulfide (15.7-39.4%) and (Z)-propenyl sec-butyl disulfide (23.4-45.0%). Ferula essential oils stimulated [Ca²⁺]_i mobilization in human neutrophils and activated ROS production in human neutrophils and murine bone marrow phagocytes. Activation of human neutrophil [Ca²⁺]_i flux by Ferula essential oils was dose-dependently inhibited by capsazepine, a TRPV1 channel antagonist, indicating that TRPV1 channels mediate this response. Furthermore, Ferula essential oils stimulated Ca²⁺ influx in TRPV1 channel-transfected HEK293 cells and desensitized the capsaicin-induced response in these cells. Additional molecular modeling with known TRPV1 channel agonists suggested that the active component is likely to be (Z)-propenyl sec-butyl disulfide. Our results provide a cellular and molecular basis to explain at least part of the beneficial therapeutic properties of FEOs.

Effect of Proline-Containing Oligopeptides PGP and RGP on Proliferative and Protein-Synthesizing Activity of Cultured Pulmonary Fibroblasts under Conditions of Oxidative Stress

We studied the effect of glyprolines Pro-Gly-Pro (PGP) and Arg-Gly-Pro (RGP) on the primary culture of pulmonary fibroblasts from newborn albino rats under normal conditions and during oxidative stress. Under physiological conditions, the peptides had no effect on parameters of cell division. Hydrogen peroxide induced intensive oxidative stress accompanied by suppression of protein-synthesizing function. When hydrogen peroxide was added to the culture containing the test peptides, correction of the oxidative status was observed accompanied by activation of DNA-synthesizing activity and inhibition of lucigenin-dependent chemiluminescence.

The Role of Hydrogen Peroxide and Other Reactive Oxygen Species in Wound Healing

Wound healing is a complex physiological process important for tissue homeostasis. An acute injury initiates massive cell migration, proliferation and differentiation, synthesis of extracellular matrix components, scar formation and remodelling. Blood flow and tissue oxygenation are parts of the complex regulation of healing. Higher organisms utilize molecular oxygen as a terminal oxidant. This way of gaining energy for vital processes such as healing leads to the production of a number of oxygen compounds that may have a defensive or informatory role. They may be harmful when present in high concentrations. Both the lack and the excess of reactive oxygen species may influence healing negatively.

The role of reactive oxygen species in mesenchymal stem cell adipogenic and osteogenic differentiation: a review

Mesenchymal stromal cells (MSCs) are promising candidates for tissue engineering and regenerative medicine. The multipotent stem cell component of MSC isolates is able to differentiate into derivatives of the mesodermal lineage including adipocytes, osteocytes, chondrocytes, and myocytes. Many common pathways have been described in the regulation of adipogenesis and osteogenesis. However, stimulation of osteogenesis appears to suppress adipogenesis and vice-versa. Increasing evidence implicates a tight regulation of these processes by reactive oxygen species (ROS). ROS are short-lived oxygen-containing molecules that display high chemical reactivity toward DNA, RNA, proteins, and lipids. Mitochondrial complexes I and III, and the NADPH oxidase isoform NOX4 are major sources of ROS production during MSC differentiation. ROS are thought to interact with several pathways that affect the transcription machinery required for MSC differentiation including the Wnt, Hedgehog, and FOXO signaling cascades. On the other hand, elevated levels of ROS, defined as oxidative stress, lead to arrest of the MSC cell cycle and apoptosis. Tightly regulated levels of ROS are therefore critical for MSC terminal differentiation, although the precise sources, localization, levels and the exact species of ROS implicated remain to be determined. This review provides a detailed overview of the influence of ROS on adipogenic and osteogenic differentiation in MSCs.

Pathophysiological importance of aggregated damaged proteins

Reactive oxygen species (ROS) are formed continuously in the organism even under physiological conditions. If the level of ROS in cells exceeds the cellular defense capacity, components such as RNA/DNA, lipids, and proteins are damaged and modified, thus affecting the functionality of organelles as well. Proteins are especially prominent targets of various modifications such as oxidation, glycation, or conjugation with products of lipid peroxidation, leading to the alteration of their biological function, nonspecific interactions, and the production of high-molecular-weight protein aggregates. To ensure the maintenance of cellular functions, two proteolytic systems are responsible for the removal of oxidized and modified proteins, especially the proteasome and organelles, mainly the autophagy-lysosomal systems. Furthermore, increased protein oxidation and oxidation-dependent impairment of proteolytic systems lead to an accumulation of oxidized proteins and finally to the formation of nondegradable protein aggregates. Accordingly, the cellular homeostasis cannot be maintained and the cellular metabolism is negatively affected. Here we address the current knowledge of protein aggregation during oxidative stress, aging, and disease.

Oxidative stress: an essential factor in the pathogenesis of gastrointestinal mucosal diseases

Reactive oxygen species (ROS) are generated as by-products of normal cellular metabolic activities. Superoxide dismutase, glutathione peroxidase, and catalase are the enzymes involved in protecting cells from the damaging effects of ROS. ROS are produced in response to ultraviolet radiation, cigarette smoking, alcohol, nonsteroidal anti-inflammatory drugs, ischemia-reperfusion injury, chronic infections, and inflammatory disorders. Disruption of normal cellular homeostasis by redox signaling may result in cardiovascular, neurodegenerative diseases and cancer. ROS are produced within the gastrointestinal (GI) tract, but their roles in pathophysiology and disease pathogenesis have not been well studied. Despite the protective barrier provided by the mucosa, ingested materials and microbial pathogens can induce oxidative injury and GI inflammatory responses involving the epithelium and immune/inflammatory cells. The pathogenesis of various GI diseases including peptic ulcers, gastrointestinal cancers, and inflammatory bowel disease is in part due to oxidative stress. Unraveling the signaling events initiated at the cellular level by oxidative free radicals as well as the physiological responses to such stress is important to better understand disease pathogenesis and to develop new therapies to manage a variety of conditions for which current therapies are not always sufficient.

Oxidative status interactome map: towards novel approaches in experiment planning, data analysis, diagnostics and therapy

Experimental evidence suggests an immense variety of processes associated with and aimed at producing reactive oxygen and/or nitrogen species. Clinical studies implicate an enormous range of pathologies associated with reactive oxygen/nitrogen species metabolism deregulation, particularly oxidative stress. Recent advances in biochemistry, proteomics and molecular biology/biophysics of cells suggest oxidative stress to be an endpoint of complex dysregulation events of conjugated pathways consolidated under the term, proposed here, "oxidative status". The oxidative status concept, in order to allow for novel diagnostic and therapeutic approaches, requires elaboration of a new logic system comprehending all the features, versatility and complexity of cellular pro- and antioxidative components of different nature. We have developed a curated and regularly updated interactive interactome map of human cellular-level oxidative status allowing for systematization of the related most up-to-date experimental data. A total of more than 600 papers were selected for the initial creation of the map. The map comprises more than 300 individual factors with respective interactions, all subdivided hierarchically for logical analysis purposes. The pilot application of the interactome map suggested several points for further development of oxidative status-based technologies.

Oleic, linoleic and linolenic acids increase ros production by fibroblasts via NADPH oxidase activation

The effect of oleic, linoleic and γ-linolenic acids on ROS production by 3T3 Swiss and Rat 1 fibroblasts was investigated. Using lucigenin-amplified chemiluminescence, a dose-dependent increase in extracellular superoxide levels was observed during the treatment of fibroblasts with oleic, linoleic and γ-linolenic acids. ROS production was dependent on the addition of β-NADH or NADPH to the medium. Diphenyleneiodonium inhibited the effect of oleic, linoleic and γ-linolenic acids on fibroblast superoxide release by 79%, 92% and 82%, respectively. Increased levels of p47^phox phosphorylation due to fatty acid treatment were detected by Western blotting analyses of fibroblast proteins. Increased p47^phox mRNA expression was observed using real-time PCR. The rank order for the fatty acid stimulation of the fibroblast oxidative burst was as follows: γ-linolenic > linoleic > oleic. In conclusion, oleic, linoleic and γ-linolenic acids stimulated ROS production via activation of the NADPH oxidase enzyme complex in fibroblasts.

OXPHOS mutations and neurodegeneration

Mitochondrial oxidative phosphorylation (OXPHOS) sustains organelle function and plays a central role in cellular energy metabolism. The OXPHOS system consists of 5 multisubunit complexes (CI-CV) that are built up of 92 different structural proteins encoded by the nuclear (nDNA) and mitochondrial DNA (mtDNA). Biogenesis of a functional OXPHOS system further requires the assistance of nDNA-encoded OXPHOS assembly factors, of which 35 are currently identified. In humans, mutations in both structural and assembly genes and in genes involved in mtDNA maintenance, replication, transcription, and translation induce 'primary' OXPHOS disorders that are associated with neurodegenerative diseases including Leigh syndrome (LS), which is probably the most classical OXPHOS disease during early childhood. Here, we present the current insights regarding function, biogenesis, regulation, and supramolecular architecture of the OXPHOS system, as well as its genetic origin. Next, we provide an inventory of OXPHOS structural and assembly genes which, when mutated, induce human neurodegenerative disorders. Finally, we discuss the consequences of mutations in OXPHOS structural and assembly genes at the single cell level and how this information has advanced our understanding of the role of OXPHOS dysfunction in neurodegeneration.

Plasma membrane electron transport in pancreatic β-cells is mediated in part by NQO1

Plasma membrane electron transport (PMET), a cytosolic/plasma membrane analog of mitochondrial electron transport, is a ubiquitous system of cytosolic and plasma membrane oxidoreductases that oxidizes cytosolic NADH and NADPH and passes electrons to extracellular targets. While PMET has been shown to play an important role in a variety of cell types, no studies exist to evaluate its function in insulin-secreting cells. Here we demonstrate the presence of robust PMET activity in primary islets and clonal β-cells, as assessed by the reduction of the plasma membrane-impermeable dyes WST-1 and ferricyanide. Because the degree of metabolic function of β-cells (reflected by the level of insulin output) increases in a glucose-dependent manner between 4 and 10 mM glucose, PMET was evaluated under these conditions. PMET activity was present at 4 mM glucose and was further stimulated at 10 mM glucose. PMET activity at 10 mM glucose was inhibited by the application of the flavoprotein inhibitor diphenylene iodonium and various antioxidants. Overexpression of cytosolic NAD(P)H-quinone oxidoreductase (NQO1) increased PMET activity in the presence of 10 mM glucose while inhibition of NQO1 by its inhibitor dicoumarol abolished this activity. Mitochondrial inhibitors rotenone, antimycin A, and potassium cyanide elevated PMET activity. Regardless of glucose levels, PMET activity was greatly enhanced by the application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle. We propose a model for the role of PMET as a regulator of glycolytic flux and an important component of the metabolic machinery in β-cells.

There is no evidence that mitochondria are the main source of reactive oxygen species in mammalian cells

It is often assumed that mitochondria are the main source of reactive oxygen species (ROS) in mammalian cells, but there is no convincing experimental evidence for this in the literature. What evidence there is suggests mitochondria are a significant source for ROS, which may have physiological and pathological effects. But quantitatively, endoplasmic reticulum and peroxisomes have a greater capacity to produce ROS than mitochondria, at least in liver. In most cells and physiological or pathological conditions there is a lack of evidence for or against mitochondria being the main source of cellular ROS. Mitochondria can rapidly degrade ROS and thus are potential sinks for ROS, but whether mitochondria act as net sources or sinks within cells in particular conditions is unknown.

Functions and regulation of the Nox family in the filamentous fungus Podospora anserina: a new role in cellulose degradation

NADPH oxidases are enzymes that produce reactive oxygen species. Studies in mammals, plants and fungi have shown that they play important roles in differentiation, defence, host/pathogen interaction and mutualistic symbiosis. In this paper, we have identified a Podospora anserina mutant strain impaired for processes controlled by PaNox1 and PaNox2, the two Nox isoforms characterized in this model ascomycete. We show that the gene mutated is PaNoxR, the homologue of the gene encoding the regulatory subunit p67(phox), conserved in mammals and fungi, and that PaNoxR regulates both PaNox1 and PaNox2. Genome sequence analysis of P. anserina reveals that this fungus posses a third Nox isoform, PaNox3, related to human Nox5/Duox and plant Rboh. We have generated a knock-out mutant of PaNox3 and report that PaNox3 plays a minor role in P. anserina, if any. We show that PaNox1 and PaNox2 play antagonist roles in cellulose degradation. Finally, we report for the first time that a saprobic fungus, P. anserina, develops special cell structures dedicated to breach and to exploit a solid cellulosic substrate, cellophane. Importantly, as for similar structures present in some plant pathogens, their proper differentiation requires PaNox1, PaNox2, PaNoxR and the tetraspanin PaPls1.

Association of plasma asymmetrical dimethylarginine (ADMA) with elevated vascular superoxide production and endothelial nitric oxide synthase uncoupling: implications for endothelial function in human atherosclerosis

BACKGROUND

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered to be a risk factor for atherosclerosis. However, the mechanisms relating ADMA with vascular function have been evaluated in vitro and in animal models, but its effect in human vasculature is unclear.

AIMS

We examined the impact of serum ADMA on endothelial nitric oxide (NO) bioavailability and vascular superoxide radical (O2-) production in patients with advanced atherosclerosis.

METHODS AND RESULTS

Paired samples of saphenous veins (SVs) and internal mammary arteries (IMAs) were collected from 201 patients undergoing coronary bypass surgery, and serum ADMA was measured pre-operatively. The vasomotor responses of SV segments to acetylcholine (ACh) and bradykinin (Bk) were evaluated ex vivo. Vascular O2- was measured in paired SV and IMA by lucigenin-enhanced chemiluminescence. The l-NAME-inhibitable as well as the NADPH-stimulated vascular O2- generation was also determined by chemiluminescence. High serum ADMA levels were associated with decreased vasorelaxation of SV to ACh (P < 0.05) and Bk (P < 0.05). Similarly, high serum ADMA was associated with higher total O2- production in both SVs and IMAs (P < 0.05) and greater L-NAME-inhibitable vascular O2- (P < 0.05). However, serum ADMA was not associated with NADPH-stimulated vascular O2-. In multivariable linear regression, serum ADMA was independently associated with vascular O2- in both SVs [beta (SE): 0.987 (0.412), P = 0.019] and IMAs [beta (SE): 1.905 (0.541), P = 0.001]. Asymmetrical dimethylarginine was also independently associated with maximum vasorelaxation in response to both ACh [beta (SE): 14.252 (3.976), P = 0.001] and Bk [beta (SE): 9.564 (3.762), P = 0.013].

CONCLUSION

This is the first study that demonstrates an association between ADMA and important measures of vascular function, such as vascular O2- production and NO bioavailability directly in human vessels. Although serum ADMA has no effect on NADPH-stimulated superoxide in intact vessels, it is associated with greater eNOS uncoupling in the human vascular endothelium of patients with coronary artery disease.

Thiol chemistry in peroxidase catalysis and redox signaling

The oxidation chemistry of thiols and disulfides of biologic relevance is described. The review focuses on the interaction and kinetics of hydrogen peroxide with low-molecular-weight thiols and protein thiols and, in particular, on sulfenic acid groups, which are recognized as key intermediates in several thiol oxidation processes. In particular, sulfenic and selenenic acids are formed during the catalytic cycle of peroxiredoxins and glutathione peroxidases, respectively. In turn, these enzymes are in close redox communication with the thioredoxin and glutathione systems, which are the major controllers of the thiol redox state. Oxidants formed in the cell originate from several different sources, but the major producers are NADPH oxidases and mitochondria. However, a different role of the oxygen species produced by these sources is apparent as oxidants derived from NADPH oxidase are involved mainly in signaling processes, whereas those produced by mitochondria induce cell death in pathways including also the thioredoxin system, presently considered an important target for cancer chemotherapy.

Mechanisms underlying caloric restriction and lifespan regulation: implications for vascular aging

This review focuses on the emerging evidence that attenuation of the production of reactive oxygen species and inhibition of inflammatory pathways play a central role in the antiaging cardiovascular effects of caloric restriction. Particular emphasis is placed on the potential role of the plasma membrane redox system in caloric restriction-induced pathways responsible for sensing oxidative stress and increasing cellular oxidative stress resistance. We propose that caloric restriction increases bioavailability of NO, decreases vascular reactive oxygen species generation, activates the Nrf2/antioxidant response element pathway, inducing reactive oxygen species detoxification systems, exerts antiinflammatory effects, and, thereby, suppresses initiation/progression of vascular disease that accompany aging.

CuZn-SOD suppresses the bovine papillomavirus-induced proliferation of fibroblasts

Eukaryotic cells continuously produce reactive oxygen species (ROS) and have mechanisms to control ROS levels. ROS have been shown to mediate cell proliferation and transformation. We studied the effect of CuZn-superoxide dismutase (CuZnSOD) on the focus-forming ability of bovine papillomavirus (BPV-1) wtDNA and hypertransforming mutant of its major oncoprotein E5, E5-17S. We found that CuZnSOD suppresses the focus-forming ability of BPV-1 wtDNA and E5 oncoprotein. Significantly fewer foci were detected in pCGCuZnSOD- and BPV-1 DNA-cotransfected cell culture compare to BPV-1 DNA-transfected cell culture (p<0.001). CuZnSOD decreases the rate of cell proliferation in both non-transformed C127 and BPV-1- and E5-transformed cell lines. CuZnSOD decelerates cell entry into the S phase of the cell cycle and has a suppressing effect on the actively dividing cells. As the transformed cells proliferate faster than normal cells when confluent, CuZnSOD inhibits the growth of foci. These results indicate that superoxide radicals may be involved in signaling for cell proliferation and that SOD suppresses cell proliferation.

The role of reactive oxygen species and nitric oxide in mast cell-dependent inflammatory processes

Reactive oxygen species (ROS) and reactive nitrogen oxide species (RNOS), including nitric oxide, are produced in cells by a variety of enzymatic and non-enzymatic mechanisms. At high levels, both types of oxidants are used to kill ingested organisms within phagocytes. At low levels, RNOS may diffuse outside cells where they impact the vasculature and nervous system. Recent evidence suggests that low levels of ROS produced within cells are involved in cell signaling. Along with these physiological roles, many pathological conditions exist where detrimental high-level ROS and RNOS are produced. Many situations in which ROS/RNOS are associated also involve mast cell activation. In innate immunity, such mast cells are involved in the immune response toward pathogens. In acquired immunity, activation of mast cells by cross-linking of receptor-bound immunoglobulin E causes the release of mediators involved in the allergic inflammatory response. In this review, we describe the principle pathways for ROS and RNOS generation by cells and discuss the existence of such pathways in mast cells. In addition, we examine the evidence for a functional role for ROS and RNOS in mast cell secretory responses and discuss evidence for a direct relationship between ROS, RNOS, and mast cells in mast cell-dependent inflammatory conditions.

Cis-unsaturated fatty acids stimulate reactive oxygen species generation and lipid peroxidation in human spermatozoa

CONTEXT

Defective sperm function is the largest defined cause of human infertility; however, the etiology of this condition is poorly understood. Although oxidative stress is acknowledged as a key contributor to this pathology, there are also data indicating that defective human spermatozoa contain abnormally high amounts of cis-unsaturated fatty acids. This study investigated whether a causative relationship exists between these two attributes of impaired semen quality.

OBJECTIVE

The objective of this study was to determine whether polyunsaturated fatty acids can induce oxidative stress in human spermatozoa.

METHOD

Dihydroethidium and SYTOX Green were used in conjunction with flow cytometry and HPLC to investigate reactive oxygen species (ROS) generation by human spermatozoa after fatty acid exposure.

RESULTS

Arachidonic acid (AA) induced a time- and dose-dependent increase in ROS generation by human spermatozoa that led to the promotion of peroxidative damage and a loss of sperm motility. This effect could not be blocked with inhibitors of the cyclooxygenase or lipoxygenase pathways of AA metabolism, rotenone, protein kinase C antagonists, or known inhibitors of plasma membrane redox systems. However, ROS generation could be triggered with other cis-unsaturated fatty acids including linoleic and docosahexaenoic acids. Saturated fatty acids, methyl esters of unsaturated fatty acids, or other amphiphiles were all ineffective. However in a cell-free system, AA could trigger a redox signal via mechanisms that were profoundly disrupted by diphenylene iodonium, a flavoprotein inhibitor.

CONCLUSIONS

The presence of excess unsaturated fatty acids in defective human spermatozoa may precipitate the oxidative stress encountered in male infertility.

Kinetic Modeling of Nitric-Oxide-Associated Reaction Network

PURPOSE

Nitric oxide and superoxide are the two important free radicals in the biological system. The coexistence of both free radicals in the physiological milieu gives rise to intricate oxidative and nitrosative reactions, which have been implicated in many physiological and/or pathophysiological conditions, such as vasodilatation and inflammation. It is difficult, if not impossible, to study the complexity of the nitric oxide/superoxide system using current experimental approaches. Computational modeling thus offers an alternative way for studying the problem.

METHODS

In this present study, key reaction pathways related to the generation, reaction and scavenging of both nitric oxide and superoxide were integrated into a reaction network. The network dynamics was investigated by numerical simulations to a set of coupled differential equations and by dynamical analysis. Two specific questions pertaining to the reaction kinetics of the reactive chemical species in the nitric oxide/superoxide system were studied: (1) how does the system respond dynamically when the generation rate of nitric oxide and superoxide varies? (2) how would antioxidants such as glutathione modulate the system dynamics?

RESULTS

While changing basal GSH levels does not alter the kinetics of nitric oxide, superoxide, and peroxynitrite, the kinetic profiles of N203, GSNO and GSH are sensitive to the variation of basal GSH levels. The kinetics of the potential nitrosative species, N203, is switch like, which is dependent on the level of GSH.

CONCLUSIONS

The model predicts that concurrent high nitric oxide and superoxide generation--such as in the inflammatory conditions--may result in nonlinear system dynamics, and glutathione may serve as a dynamic switch of N203 mediated nitrosation reaction.

Bovine papillomavirus type 1 oncoprotein E5 stimulates the utilization of superoxide radicals in the mouse fibroblast cell line C127

The major transforming protein of bovine papillomavirus type 1 (BPV-1) is a small hydrophobic polypeptide, the E5 gene product, localized in the cellular membranes and modulating various pathways in the cell. Many studies have shown that reactive oxygen species (ROS) are essential in several biological processes, including cell transformation by oncogenes, but unregulated ROS are highly toxic to cells. We studied the effect of the bovine papillomavirus protein E5 and its mutants on the level of the superoxide radicals in the mouse fibroblast cell line C127. The superoxide level in C127 cells transfected with the E5-expressing plasmids were measured by nitroblue tetrazolium reduction. Relative concentrations of intracellular peroxide were determined by using 2,7-dichlorofluorescin diacetate. Our results showed that all transforming mutants of E5 reduced the level of superoxide in C127 cells, besides the activity of superoxide dismutase (SOD) and level of peroxides was not altered. In the presence of neopterin, an inhibitor of the superoxide-producing enzymes, the reduction of superoxide level correlated with the transforming ability of the E5-mutants. The inhibitor of the protein tyrosine kinase, tyrphostin 25 and inhibitors of oxygenases of the arachidonic acid metabolism, aspirin and nordihydroguaiaretic acid, blocked the effect of BPV-1 E5. We conclude that BPV-1 E5 and its transforming mutants are able to modulate the level of superoxide and stimulate the utilization of superoxide through protein tyrosine kinases and oxygenases of the arachidonic acid metabolism.

The modulation of thiol redox state affects the production and metabolism of hydrogen peroxide by heart mitochondria

In rat heart mitochondria, auranofin, arsenite, diamide, and BCNU increase H2O2 formation, further stimulated by antimycin. However, in submitochondrial particles, H2O2 formation and oxygen uptake are not affected, indicating that these substances do not alter respiration. Mitochondria are also able to rapidly metabolize added H2O2 in a process partially prevented by BCNU or auranofin. Calcium does not modify the production of H2O2 and the mitochondrial thioredoxin system is not affected by calcium ions. Auranofin, arsenite, and diamide determine a large mitochondrial permeability transition, while BCNU and acetoacetate are ineffective. Thiols and glutathione are modified only by BCNU and diamide. However, all the compounds tested cause the release of cytochrome c that occurs also in the absence of mitochondrial swelling. In conclusion, the compounds utilized share the common feature of shifting the mitochondrial thiol-linked redox balance towards a more oxidized condition that is responsible of the observed effects.

Free Radical Mechanisms of Aging Processes Under Physiological Conditions

Free radical theory of aging predicts crucial role for free radicals produced by external factors (environmental contamination, irradiation, etc.) or pathological disorders (hereditary diseases or infections) in the initiation of aging. Does it mean that under hypothetical completely physiological conditions aging processes could be fully suppressed? To answer this question, we will consider the possible mechanisms of free radical formation in such hypothetical state. There are two major mechanisms, which are responsible for free radical-mediated damage in a living organism: superoxide overproduction by mitochondria and nonenzymatic lipid peroxidation. Superoxide overproduction causes the inhibition of nitric oxide formation and bioavailability, one of principal characteristics of aging, while nonenzymatic lipid peroxidation, which is already demonstrated at physiological conditions, produces toxic isoprostanes. We suggest that major initiators of free radical-mediated damaging processes leading to aging at physiological state are oxidizable components of diet. The possibility of inhibition of aging processes by supplementation of nontoxic antioxidants and calorie restriction is discussed. Scheme demonstrating the potential mechanisms of starting the free radical-mediated aging processes is presented, which are discussed on the grounds of known literature data.

The plasma membrane redox system: a candidate source of aging-related oxidative stress

The plasma membrane redox system (PMRS) is an electron transport chain in the plasma membrane that transfers electrons from either intra- or extracellular donors to extracellular acceptors. Unlike the superoxide-generating NADPH oxidase of phagocytes and the homologous (but much less active) enzymes found in some other cells, the PMRS is still incompletely characterised at the molecular level. Much is known, however, concerning its function and affinity for both physiological and non-physiological substrates. A role for it in aging, the 'reductive hotspot hypothesis' (RHH), was proposed in 1998 as part of an explanation for the apparently indefinite survival in vivo of cells that have entirely lost mitochondrial respiratory capacity as a result of the accumulation of mitochondrial mutations. Stimulation of the PMRS might allow the cell to maintain redox homeostasis even while continuing to operate the Krebs cycle, which may be advantageous in many ways. However, the PMRS may, like the mitochondrial respiratory chain, be prone to generate superoxide when thus dysregulated - and in this case superoxide would be generated outside the cell, where antioxidant defences are more limited than inside the cell and where much highly oxidisable material is present. Cascades of peroxidation chain reactions initiated by this process may greatly amplify the oxidative stress on the organism that is caused by rare mitochondrially mutant cells. Since such cells increase in abundance with aging (though remaining rare), this is an economical hypothesis to explain the rise in oxidative stress seen in (and generally believed to contribute substantially to) mammalian aging. In an extension of previously published accounts of RHH, I propose here that the lysosomal toxicity of oxidised cholesterol derivatives (oxysterols) may contribute to the toxicity of mitochondrial mutations by affecting lysosomal function in many cell types in the same way as they have been proposed to do in arterial macrophages.

Lipoxygenase-dependent superoxide release in skeletal muscle

Superoxide anion radical (O2•−) is released from skeletal muscle at rest and is particularly elevated during conditions of heat stress (42°C). Previous studies have shown that in isolated rat diaphragm O2•−release is not dependent on mitochondrial electron transport, reduced NADP oxidase activity, or the integrity of membrane anion channels. This study hypothesized that O2•−release, as measured by cytochrome c reduction, is linked to metabolism of arachidonic acid. Phospholipase A2inhibition with manoalide significantly decreased O2•−release. In downstream pathways, neither the blockage of cyclooxygenase with indomethacin nor the inhibition of cytochrome P-450-dependent monooxygenase with SKF-525A decreased O2•−release. However, lipoxygenase (LOX) inhibition with general LOX blockers 5,8,11,14-eicosatetraynoic acid and cinnamyl-3,4-dihydroxy-α-cyanocinnamate greatly attenuated the signal. Furthermore, the specific 5-LOX inhibitor diethylcarbamazine also significantly decreased O2•−release. Immunohistochemistry localized 5- and 12-LOX to the cytosol and sarcolemma of muscle cells. Confocal studies, using the O2•−-sensitive fluorescent indicator hydroethidine, demonstrated that LOX inhibition had no significant influence on intracellular O2•−formation. When compared with the cytochrome c results, this indicates that intra- and extracellular O2•−must arise from different sources. These data show for the first time that arachidonic acid metabolism through LOX activity, is a major source of extracellular O2•−release in skeletal muscle.

GTPases and reactive oxygen species: switches for killing and signaling

In neutrophils and other phagocytic cells, the small GTPase Rac is an essential regulator of a multi-component NADPH oxidase that produces high levels of superoxide, which kills invading pathogens. In many other cell types, Rac and newly discovered relatives of the neutrophil burst oxidase and its subunits have been found associated with production of reactive oxygen species, implicating superoxide production in a wide range of cellular processes not related to host defense. Although the precise role played by Rac in the regulation of these novel oxidases is not known, Rac does control the cellular redox state. Through these pro-oxidant mechanisms, Rac and the novel oxidases modify gene expression, cell proliferation, adhesion and many cell-specific functions.

Arachidonic acid triggers an oxidative burst in leukocytes

The change in cellular reducing potential, most likely reflecting an oxidative burst, was investigated in arachidonic acid- (AA) stimulated leukocytes. The cells studied included the human leukemia cell lines HL-60 (undifferentiated and differentiated into macrophage-like and polymorphonuclear-like cells), Jurkat and Raji, and thymocytes and macrophages from rat primary cultures. The oxidative burst was assessed by nitroblue tetrazolium reduction. AA increased the oxidative burst until an optimum AA concentration was reached and the burst decreased thereafter. In the leukemia cell lines, optimum concentration ranged from 200 to 400 microM (up to 16-fold), whereas in rat cells it varied from 10 to 20 microM. Initial rates of superoxide generation were high, decreasing steadily and ceasing about 2 h post-treatment. The continuous presence of AA was not needed to stimulate superoxide generation. It seems that the NADPH oxidase system participates in AA-stimulated superoxide production in these cells since the oxidative burst was stimulated by NADPH and inhibited by N-ethylmaleimide, diphenyleneiodonium and superoxide dismutase. Some of the effects of AA on the oxidative burst may be due to its detergent action. There apparently was no contribution of other superoxide-generating systems such as xanthine-xanthine oxidase, cytochromes p-450 and mitochondrial electron transport chain, as assessed by the use of inhibitors. Eicosanoids and nitric oxide also do not seem to interfere with the AA-stimulated oxidative burst since there was no systematic effect of cyclooxygenase, lipoxygenase or nitric oxide synthase inhibitors, but lipid peroxides may play a role, as indicated by the inhibition of nitroblue tetrazolium reduction promoted by tocopherol.

X radiation causes a persistent induction of reactive oxygen species and a delayed reinduction of TP53 in normal human diploid fibroblasts

Multiple genetic changes are required for the development of a malignant cell. The frequency of such changes in cancer cells is higher than can be explained through random mutation, and it was proposed that a subpopulation of cells develop a persistent mutator phenotype. Evidence for such a phenotype has been observed in mammalian cells after treatment with ionizing radiation. The mechanism that promotes this effect has not been defined, but proposed explanations include increased levels of reactive oxygen species (ROS) in irradiated cells and their progeny. The tumor suppressor TP53 is of prime importance in coordinating the cellular response to damage, and it has been suggested to have a role in regulating the cellular redox state. We investigated the persistence of induced levels of ROS in normal diploid human cells for 1 month after X-ray exposure and the role of TP53 in this oxidant response. X radiation induced an oxidant response that persisted for 2 weeks after exposure in cells with normal TP53 function. ROS levels in cells with abrogated TP53 function were decreased in magnitude and duration. X radiation caused a primary transient induction of TP53 followed by a reinduction of TP53 5 days after irradiation. This reinduction persisted for at least 2 days and coincided with the largest induction of apoptosis. The persistently elevated levels of ROS and delayed reinduction of TP53 reported here are further evidence of the delayed effects of ionizing radiation and add to the growing number of such observations.

HO2*: the forgotten radical

HO2*, usually termed either hydroperoxyl radical or perhydroxyl radical, is the protonated form of superoxide; the protonation/deprotonation equilibrium exhibits a pK(a) of around 4.8. Consequently, about 0.3% of any superoxide present in the cytosol of a typical cell is in the protonated form. This ratio is rather accurately reflected by the published literature on the two species, as identified by a PubMed search; at the time of writing only 28 articles mention "HO2," "hydroperoxyl" or "perhydroxyl" in their titles, as against 9228 mentioning superoxide. Here it is argued that this correlation is not justifiable: that HO2*'s biological and biomedical importance far exceeds the attention it has received. Several key observations of recent years are reviewed that can be explained much more economically when the participation of HO2* is postulated. It is suggested that a more widespread appreciation of the possible role of HO2* in biological systems would be of considerable benefit to biomedical research.

The reductive hotspot hypothesis of mammalian aging: membrane metabolism magnifies mutant mitochondrial mischief

A severe challenge to the idea that mitochondrial DNA mutations play a major role in the aging process in mammals is that clear loss-of-function mutations accumulate only to very low levels (under 1% of total) in almost any tissue, even by very old age. Their accumulation is punctate: some cells become nearly devoid of wild-type mitochondrial DNA and exhibit no activity for the partly mitochondrially encoded enzyme cytochrome c oxidase. Such cells accumulate in number with aging, suggesting that they survive indefinitely, which is itself paradoxical. The reductive hotspot hypothesis suggests that these cells adjust their metabolism to use plasma membrane electron transport as a substitute for the mitochondrial electron transport chain in the reoxidation of reduced dinucleotides, and that, like mitochondrial electron transport, this process is imperfect and generates superoxide as a side-effect. This superoxide, generated on the outside of the cell, can potentially initiate classical free radical chemistry including lipid peroxidation chain reactions in circulating material such as lipoproteins. These, in turn, can be toxic to mitochondrially nonmutant cells that import them to satisfy their cholesterol requirements. Thus, the relatively few cells that have lost oxidative phosphorylation capacity may be toxic to the rest of the body. In this minireview, recent results relevant to this hypothesis are surveyed and approaches to intervening in the proposed process are discussed.

Superoxide mediates shock wave induction of ERK-dependent osteogenic transcription factor (CBFA1) and mesenchymal cell differentiation toward osteoprogenitors

Extracorporeal shock wave (ESW) is an alternative non-invasive method for the promotion of bone growth and tendon repair. In an animal model, we have reported that ESW promoted bone marrow osteoprogenitor growth through transforming growth factor-beta1 induction. We have further explored the mechanism for the ESW promotion of osteogenesis. Results showed that an optimal ESW treatment at 0.16 mJ/mm(2) for 500 impulses rapidly induced a higher O(2)(-) and ONOO(-) production associated with a decrease of nitric oxide level in 1 h, and induced a higher transforming growth factor-beta1 production in 24 h, and a higher colony-forming units-osteoprogenitor formation in 12 days. The colony-forming units-osteoprogenitor colonies revealed positive staining of bone alkaline phosphatase and turned into bone nodules in 21 days. Early scavenging of O(2)(-) but not Ca(2+), H(2)O(2), or prostaglandin E(2) suppressed osteoprogenitor cell growth and maturation. Scavenging of O(2)(-) by superoxide dismutase raised the nitric oxide level back to the basal level and suppressed ESW-promoted osteoprogenitor cell growth, whereas inhibition of ONOO(-) by urate or NO by N-nitro-l-arginine methyl ester did not affect ESW promotion of osteogenesis, indicating that O(2)(-) acted as an early signal for ESW-induced cell growth. Further studies demonstrated that ESW induced ERK activation, and blockage of O(2)(-) production or inhibition of tyrosine kinase, but not protein kinase A and C inhibitors, suppressed ESW-induced ERK activation. In support that O(2)(-) mediated the ESW-induced ERK activation and osteogenic differentiation, we further demonstrated that scavenging of O(2)(-) by superoxide dismutase and inhibition of ERK activation by PD98059 decreased specific osteogenic transcription factor, core binding factor A1 activation, and decreased osteocalcin expression. Taken together, we showed that ESW-induced O(2)(-) production followed by tyrosine kinase-mediated ERK activation and core binding factor A1 activation resulted in osteogenic cell growth and maturation. Thus, an appropriate modulation of redox reaction by ESW may have some positive effect on the bone regeneration.

Impact of inhibition of complement by sCR1 on hepatic microcirculation after warm ischemia

Recent observations provide evidence that complement is implicated as an important factor in the pathophysiology of ischemia/reperfusion injury (IRI). Here, we assessed the effects of complement inhibition on hepatic microcirculation by in vivo microscopy (IVM) using a rat model of warm hepatic ischemia clamping the left pedicle for 70 min. Ten animals received the physiological complement regulator soluble complement receptor type 1 (sCR1) intravenously 1 min prior to reperfusion. Controls were given an equal amount of Ringer's solution (n = 10). Microvascular perfusion and leukocyte adhesion were studied 30 to 100 min after reperfusion by IVM. Microvascular perfusion in hepatic sinusoids was significantly improved in the sCR1 group (80.6 +/- 0.6% of all observed sinusoids were perfused [sCR1] vs 67.3 +/- 1.2% [controls]). The number of adherent leukocytes was reduced in sinusoids (49.9 +/- 3.4 [sCR1] vs 312.3 +/- 14.2 in controls [adherent leukocytes per square millimeter of liver surface]; P < 0.001) as well as in postsinusoidal venules after sCR1 treatment (230.9 +/- 21.7 [sCR1] vs 1906.5 +/- 93.5 [controls] [adherent leukocytes per square millimeter of endothelial surface]; P < 0.001). Reflecting reduced hepatocyte injury, liver transaminases were decreased significantly upon sCR1 treatment compared to controls. Our results provide further evidence that complement plays a decisive role in warm hepatic IRI. Therefore, we conclude that complement inhibition by sCR1 is effective as a therapeutical approach to reduce microcirculatory disorders after reperfusion following warm organ ischemia.

Superoxide is responsible for apoptosis in rat vascular smooth muscle cells induced by alpha-tocopheryl hemisuccinate

We investigated the mechanism of cell toxicity of alpha-tocopheryl hemisuccinate (TS). TS concentration- and time-dependently induced the lactate dehydrogenase release and DNA fragmentation of rat vascular smooth muscle cells (VSMC). Exogenous addition of superoxide dismutase, but not catalase, significantly inhibited the cell toxicity of TS. The NADPH-dependent oxidase activity of VSMC was stimulated by TS treatment. The cell toxicity of TS was inhibited by NADPH oxidase inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride. Consequently, TS-induced apoptosis of VSMC was suggested to be caused by exogenous O(2)(-) generated via the oxidase system activated with TS.

Lipid peroxidation in aging and age-dependent diseases

Aging is related with an increase in oxidation products derived from nucleic acids, sugars, sterols and lipids. Evidence will be presented that these different oxidation products are generated by processes induced by changes in the cell membrane structure (CMS), and not by superoxide, as commonly assumed. CMS activate apparently membrane bound phospholipases A2 in mammals and plants. Such changes occur by proliferation, aging and especially by wounding. After activation of phospholipases, influx of Ca2+ ions and activation of lipoxygenases (LOX) is induced. The LOX transform polyunsaturated fatty acids (PUFAs) into lipid hydroperoxides (LOOHs), which seem to be decomposed by action of enzymes to signalling compounds. Following severe cell injury, LOX commit suicide. Their suicide liberates iron ions that induce nonenzymic lipid peroxidation (LPO) processes by generation of radicals. Radicals attack all compounds with the structural element -CH=CH-CH(2)-CH=CH-. Thus, they act on all PUFAs independently either in free or conjugated form. The most abundant LPO products are derived from linoleic acid. Radicals induce generation of peroxyl radicals, which oxidise a great variety of biological compounds including proteins and nucleic acids. Nonenzymic LPO processes are induced artificially by the treatment of pure PUFAs with bivalent metal ions. The products are separable after appropriate derivatisation by gas chromatography (GC). They are identified by electron impact mass spectrometry (EI/MS). The complete spectrum of LPO products obtained by artificial LPO of linoleic acid is detectable after wounding of tissue, in aged individuals and in patients suffering from age-dependent diseases. Genesis of different LPO products derived from linoleic acid will be discussed in detail. Some of the LPO products are of high chemical reactivity and therefore escape detection in biological surrounding. For instance, epoxides and highly unsaturated aldehydic compounds that apparently induce apoptosis.

Enhanced superoxide anion formation in vascular tissues from spontaneously hypertensive and desoxycorticosterone acetate-salt hypertensive rats

OBJECTIVES

To investigate the basal and NADH-stimulated superoxide (.O2-) production and inactivation by Cu/Zn superoxide dismutase (SOD) in aorta from spontaneously hypertensive rats (SHR) and from desoxycorticosterone acetate (DOCA)-salt hypertensive (DOCA-HT) rats.

METHODS

Tissue .O2- levels were estimated with the lucigenin-enhanced chemiluminescence method in aorta and cultured smooth muscle cells (SMCs) from SHR and in aorta from DOCA-HT rats treated for 4 weeks.

RESULTS

The basal aortic .O2- generation was increased by 135 and 100%, and the NADH stimulated .O2- production was also increased 37 and 22% in SHR and in DOCA-HT rats compared to their normotensive controls, respectively. Although no difference existed in blood pressure as well as in basal and in NADH stimulated .O2- production between Wistar-Kyoto (WKY) rats and SHR rats at age of 6 weeks, O2- production and blood pressure increased concomitantly in SHR aged 9 and 12 weeks. Basal and NADH-stimulated .O2- production, in cultured SMCs, was also 80 and 64% higher, respectively, in SHR compared to WKY rats. The NADH oxidase activity was found to be increased in aorta from both SHR and DOCA-HT rats but SOD activity was reduced only in aorta from DOCA-HT rats.

CONCLUSIONS

An enhanced .O2- formation resulting from an increased NADH oxidase activity was found in aorta from SHR and DOCA-HT rats. Cultured arterial SMCs from SHR also generated excessive .O2- formation under basal and stimulated conditions. The age-related increase in vascular .O2- formation in association with the rise in blood pressure in SHR suggests that the oxidative stress might contribute to the development of hypertension. NADH oxidase activity was greater in aorta of both hypertension models, but a decrease of Cu/Zn SOD activity could also contribute to the high level of aortic .O2- in DOCA-HT rats.

Superoxide generation of phagocytes and nonphagocytic cells

Phagocytes release high amounts of reactive oxygen intermediates upon contact with appropriate stimuli into the environment as an important function in the immune defence against infectious agents. On the other hand nonphagocytic cells release low amounts upon stimulation, which have important functions in the inter- and intracellular signal transduction. Both systems represent a class of isoenzymes making a specific regulation possible. Fibroblasts, hepatocytes, and HeLa cells possess a superoxide system which shows higher activity with NADH than NADPH. The enzyme was purified to homogeneity in an active form, showed a molecular mass of 84 kDa and possessed a flavin and low-potential cytochrome b558.

Vibrio fischeri genes hvnA and hvnB encode secreted NAD(+)-glycohydrolases

HvnA and HvnB are proteins secreted by Vibrio fischeri ES114, an extracellular light organ symbiont of the squid Euprymna scolopes, that catalyze the transfer of ADP-ribose from NAD(+) to polyarginine. Based on this activity, HvnA and HvnB were presumptively designated mono-ADP-ribosyltransferases (ARTases), and it was hypothesized that they mediate bacterium-host signaling. We have cloned hvnA and hvnB from strain ES114. hvnA appears to be expressed as part of a four-gene operon, whereas hvnB is monocistronic. The predicted HvnA and HvnB amino acid sequences are 46% identical to one another and share 44% and 34% identity, respectively, with an open reading frame present in the Pseudomonas aeruginosa genome. Four lines of evidence indicate that HvnA and HvnB mediate polyarginine ADP-ribosylation not by ARTase activity, but indirectly through an NAD(+)-glycohydrolase (NADase) activity that releases free, reactive, ADP-ribose: (i) like other NADases, and in contrast to the ARTase cholera toxin, HvnA and HvnB catalyzed ribosylation of not only polyarginine but also polylysine and polyhistidine, and ribosylation was inhibited by hydroxylamine; (ii) HvnA and HvnB cleaved 1, N(6)-etheno-NAD(+) and NAD(+); (iii) incubation of HvnA and HvnB with [(32)P]NAD(+) resulted in the production of ADP-ribose; and (iv) purified HvnA displayed an NADase V(max) of 400 mol min(-1) mol(-1), which is within the range reported for other NADases and 10(2)- to 10(4)-fold higher than the minor NADase activity reported in bacterial ARTase toxins. Construction and analysis of an hvnA hvnB mutant revealed no other NADase activity in culture supernatants of V. fischeri, and this mutant initiated the light organ symbiosis and triggered regression of the light organ ciliated epithelium in a manner similar to that for the wild type.

A redox signaling mechanism for density-dependent inhibition of cell growth

Reactive oxygen species (ROS) have recently drawn significant attention as putative mitogenic mediators downstream of activated growth factor receptors and oncogenic Ras; however, the possibility that a redox-related mechanism also operates in the negative control of cell proliferation by inhibitory signals has not been investigated thus far. Here we show that the arrest of growth induced by cell confluence ("contact inhibition") is due, at least in part, to a decrease in the steady-state levels of intracellular ROS and the consequent impairment of mitogenic redox signaling. In confluent fibroblast cultures, the decrease in the concentration of oxygen species was associated with diminished activity of the small GTPase Rac-1, a signal transducer directly involved in the ligand-dependent generation of oxygen-derived molecules, and was effectively mimicked by exposure of sparse cultures to dithiothreitol (DTT) and inhibitors of enzymes (phospholipase A2 and lipoxygenase) acting in the arachidonic acid cascade downstream of growth factor receptors and Rac-1. Sparse fibroblasts treated with nontoxic amounts of DTT underwent growth arrest, whereas a low concentration of hydrogen peroxide significantly increased thymidine incorporation in confluent cultures, demonstrating a causal link between redox changes and growth control by cell density. Removal of oxygen species from sparse cultures was accompanied by a drastic decrease of protein tyrosine phosphorylation after epidermal growth factor stimulation, which, at a biochemical level, reproduced the signaling hallmarks of contact inhibition. Moreover, the cytosolic tyrosine phosphatase SHP-2 was identified as a putative target for redox signaling by cell density because the enzyme itself and the associated substrates appear markedly dephosphorylated in both confluent and reductant-treated cells after exposure to epidermal growth factor, and SHP-2 enzymatic activity is strongly activated by DTT in vitro. Taken together, these data support a model in which impaired generation of ROS and increased protein tyrosine phosphatase activity impede mitogenic signaling in contact-inhibited cells.

Reactive oxygen species in cell signaling

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When cellular production of ROS overwhelms its antioxidant capacity, damage to cellular macromolecules such as lipids, protein, and DNA may ensue. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of human diseases including those of the lung. Recent studies have also implicated ROS that are generated by specialized plasma membrane oxidases in normal physiological signaling by growth factors and cytokines. In this review, we examine the evidence for ligand-induced generation of ROS, its cellular sources, and the signaling pathways that are activated. Emerging concepts on the mechanisms of signal transduction by ROS that involve alterations in cellular redox state and oxidative modifications of proteins are also discussed.

Vascular superoxide production by NAD(P)H oxidase: association with endothelial dysfunction and clinical risk factors

Superoxide anion plays important roles in vascular disease states. Increased superoxide production contributes to reduced nitric oxide (NO) bioactivity and endothelial dysfunction in experimental models of vascular disease. We measured superoxide production by NAD(P)H oxidase in human blood vessels and examined the relationships between NAD(P)H oxidase activity, NO-mediated endothelial function, and clinical risk factors for atherosclerosis. Endothelium-dependent vasorelaxations and direct measurements of vascular superoxide production were determined in human saphenous veins obtained from 133 patients with coronary artery disease and identified risk factors. The predominant source of vascular superoxide production was an NAD(P)H-dependent oxidase. Increased vascular NAD(P)H oxidase activity was associated with reduced NO-mediated vasorelaxation. Furthermore, reduced endothelial vasorelaxations and increased vascular NAD(P)H oxidase activity were both associated with increased clinical risk factors for atherosclerosis. Diabetes and hypercholesterolemia were independently associated with increased NADH-dependent superoxide production. The association of increased vascular NAD(P)H oxidase activity with endothelial dysfunction and with clinical risk factors suggests an important role for NAD(P)H oxidase-mediated superoxide production in human atherosclerosis. The full text of this article is available at http://www.circresaha.org.

NAD(P)H oxidase: role in cardiovascular biology and disease

Reactive oxygen species have emerged as important molecules in cardiovascular function. Recent work has shown that NAD(P)H oxidases are major sources of superoxide in vascular cells and myocytes. The biochemical characterization, activation paradigms, structure, and function of this enzyme are now partly understood. Vascular NAD(P)H oxidases share some, but not all, characteristics of the neutrophil enzyme. In response to growth factors and cytokines, they produce superoxide, which is metabolized to hydrogen peroxide, and both of these reactive oxygen species serve as second messengers to activate multiple intracellular signaling pathways. The vascular NAD(P)H oxidases have been found to be essential in the physiological response of vascular cells, including growth, migration, and modification of the extracellular matrix. They have also been linked to hypertension and to pathological states associated with uncontrolled growth and inflammation, such as atherosclerosis.

Cell-surface NAD(P)H-oxidase: relationship to trans-plasma membrane NADH-oxidoreductase and a potential source of circulating NADH-oxidase

The surface of mammalian cells faces an oxidizing environment that has the potential to damage proteins, lipids, and carbohydrates to which it is exposed. In contrast, the cytoplasm is reducing and its redox state is tightly regulated. Trans-plasma membrane oxidoreductases that shift electrons from cytosolic NADH to external electron acceptors such as oxygen are widely involved in cellular redox control. They reduce oxygen to water and may generate reactive oxygen species such as superoxide and hydrogen peroxide. In addition, external NAD(P)H-oxidases have been demonstrated on intact cells and as eluted proteins, but the relationship between trans-plasma membrane NADH-oxidoreductases and cell-surface NAD(P)H-oxidases is not known. To investigate further the relationship between plasma membrane NAD(P)H-oxidoreductases, and to gain insight into the physiological functions of these redox active membrane proteins, we have adapted a simple colorimetric assay for measuring the trans-plasma membrane NADH-oxidoreductase activity of viable cells to measure NAD(P)H-oxidase at the cell surface in real time. Using the cell-impermeable tetrazolium salt WST-1 in the presence of NADH or NADPH, but in the absence of an intermediate electron acceptor, we show that cell-surface NAD(P)H-oxidase is widely expressed on mammalian cells, being more abundant on rapidly proliferating cells than on resting neutrophils and spleen cells. The ratio of cofactor dependence of NAD(P)H-oxidase (NADH:NADPH) varied widely between different cells (0.7-5.2), suggesting a family of cell surface oxidases or that the activity of these enzymes may be modulated in various ways. Comparison of NAD(P)H-oxidase on the surface of viable cells with trans-membrane NADH-oxidoreductase, measured with WST-1 in the presence of 1-methoxy PMS, showed that cell-surface NAD(P)H-oxidase was differentially inhibited by the cell-impermeable thiol-blocking agent pCMBS, but was unaffected or stimulated by other thiol blocking agents. Capsaicin, which inhibits trans-plasma membrane NADH-oxidoreductase activity, stimulated surface NAD(P)H-oxidase. Metabolic inhibitors had little effect on surface NAD(P)H-oxidase activity but inhibited trans-plasma membrane activity. These results do not support the view the surface NAD(P)H-oxidase is a terminal oxidase for trans-plasma membrane NADH-oxidoreductase.