Signalling by O2-. and NO.: how far can either radical, or any specific reaction product, transmit a message under in vivo conditions?

Influence of ionizing radiation and cell density on the kinetics of autocrine destruction and intercellular induction of apoptosis in precancerous cells

Intercellular induction of apoptosis (IIA) represents a well-defined signaling model by which precancerous cells are selectively eradicated through reactive oxygen/nitrogen species and cytokine signaling from neighbour normal cells. Previously, we demonstrated that the IIA process could be enhanced by exposure of normal cells to very low doses of ionizing radiation as a result of perturbing the intercellular signaling. In this study, we investigate the kinetic behaviour of both autocrine destruction (AD) and IIA as a function of cell density of both precancerous and normal cells using an insert co-culture system and how exposure of normal cells to ionizing radiation influence the kinetics of apoptosis induction in precancerous cells. Increasing the seeding density of transformed cells shifts the kinetics of AD towards earlier times with the response plateauing only at high seeding densities. Likewise, when co-culturing precancerous cells with normal cells, increasing the seeding density of either normal or precancerous cells also shifts the kinetics of IIA response towards earlier times and plateau only at higher seeding densities. Irradiation of normal cells prior to co-culture further enhances the kinetics of IIA response, with the degree of enhancement dependent on the relative cell densities. These results demonstrate the pivotal role of the cell seeding density of normal and precancerous cells in modulating both AD and IIA. These results further support the proposition that ionizing radiation could result in an enhancement in the rate of removal of precancerous cells through the IIA process.

Inhibition of Membrane-Associated Catalase, Extracellular ROS/RNS Signaling and Aquaporin/H2O2-Mediated Intracellular Glutathione Depletion Cooperate during Apoptosis Induction in the Human Gastric Carcinoma Cell Line MKN-45

The human gastric carcinoma cell line MKN-45 is a prototype of bona fide tumor cells, as it is protected from the NADPH oxidase-1 (NOX-1)-driven HOCl- and nitric oxide (NO)/peroxynitrite apoptosis-inducing signaling pathways by a membrane-associated catalase. The use of inhibitors/scavengers shows that inhibition of membrane-associated catalase is sufficient for the activation of NO/peroxynitrite or HOCl signaling. However, this signaling is not sufficient for apoptosis induction, as intracellular glutathione peroxidase/glutathione counteracts these signaling effects. Therefore, intrusion of extracellular tumor cell-derived H₂O₂ through aquaporins is required for the full apoptosis-inducing effect of extracellular reactive oxygen/nitrogen species. This secondary step in apoptosis induction can be prevented by inhibition of aquaporins, inhibition of NOX1 and decomposition of H₂O₂. Pretreatment with inhibitors of glutathione synthase or the cysteine-glutamine antiporter (xC transporter) abrogate the requirement for aquaporin/H₂O₂-mediated glutathione depletion, thus demonstrating that intracellular glutathione is the target of intruding H₂O₂. These data allow definition of mechanistic interactions between ROS/RNS signaling after inhibition of membrane-associated catalase, the sensitizing effects of aquaporins/H₂O₂ and the counteraction of the xC transporter/glutathione synthase system. Knowledge of these mechanistic interactions is required for the understanding of selective apoptosis induction in tumor cells through reestablishment of apoptosis-inducing ROS/RNS signaling.

Bystander Effect Induced in Breast Cancer (MCF-7) and Human Osteoblast Cell Lines (hFOB 1.19) with HDR-Brachytherapy

Background:

Radiation induced bystander effects (RIBEs) occurs in unirradiated cells exhibiting indirect biological effect as a consequence of signals from other irradiated cells in the population.

Objective:

In this study, bystander effects in MCF-7 breast cancer cells and hFOB 1.19 normal osteoblast cells irradiated with gamma emitting HDR Brachytherapy Ir-192 source were investigated.

Material and Methods:

In this in-vitro study, bystander effect stimulation was conducted using medium transfer technique of irradiated cells to the non-irradiated bystander cells. Cell viability, reactive oxygen species (ROS) generation and colony forming assay was employed to evaluate the effect.

Results:

Results indicate that the exposure to the medium irradiated MCF-7 induced significant bystander killing and decreased the survival fraction of bystander MCF-7 and hFOB from 1.19 to 81.70 % and 65.44 %, respectively. A significant decrease in survival fraction was observed for hFOB 1.19 bystander cells (p < 0.05). We found that the rate of hFOB 1.19 cell growth significantly decreases to 85.5% when added with media from irradiated cells. The ROS levels of bystander cells for both cell lines were observed to have an increase even after 4 h of treatment. Our results suggest the presence of bystander effects in unirradiated cells exposed to the irradiated medium.

Conclusion:

These data provide evidence that irradiated MCF-7 breast cancer cells can induce bystander death in unirradiated MCF-7 and hFOB 1.19 bystander cells. Increase in cell death could also be mediated by the ROS generation during the irradiation with HDR brachytherapy.

MECHANISTIC MODELING PREDICTS ANTI-CARCINOGENIC RADIATION EFFECTS ON INTERCELLULAR SIGNALING IN VITRO TURN PRO-CARCINOGENIC IN VIVO

Oncogenic transformed cells represent an in vitro system mimicking early-stage carcinogenesis. These precancerous cells are subject to a selective removal via apoptosis induced by neighbor cells. By modulating the underpinning intercellular signaling mediated by cytokines and reactive oxygen/nitrogen species, ionizing radiation enhances this removal of precancerous cells in vitro, at doses from a few mGy to a few Gy. However, epidemiological data demonstrate that radiation exposure induces cancer, at least above 100 mGy. Mechanistic modeling of the given anti-carcinogenic process explains this discrepancy: The model reproduces in vitro data on apoptosis and its enhancement by radiation. For in vivo-like conditions with signal lifetimes shorter and cell densities higher than in vitro, radiation is predicted to reduce this anti-carcinogenic mechanism. Early-stage lesions that would be turned dormant or completely removed may grow large and escape this control mechanism upon irradiation.

Microsensor systems for cell metabolism - from 2D culture to organ-on-chip

Microsensor systems for cell metabolism are essential tools for investigation and standardization in cell culture. Electrochemical and optical read-out schemes dominate, which enable the marker-free, continuous, online recording of transient effects and deliver information beyond microscopy and end-point tests. There has been much progress in microfluidics and microsensors, but the translation of both into standard cell culture procedures is still limited. Within this critical review, we discuss different cell culture formats ranging from standard culture vessels to dedicated microfluidic platforms. Key aspects are the appropriate supply of cells, mass transport of metabolites to the sensors and generation of stimuli. Microfluidics enable the transition from static to dynamic conditions in culture and measurement. We illustrate the parameters oxygen (respiration), pH (acidification), glucose and lactate (energy metabolism) as well as short-lived reactive species (ROS/RNS) from the perspective of microsensor integration in 2D and 3D cell culture. We discuss different sensor principles and types, along with their limitations, microfabrication technologies and materials. The state-of-the-art of microsensor platforms for cell culture is discussed with respect to sensor performance, the number of parameters and timescale of application. That includes the advances from 2D culture to the increasingly important 3D approaches, with specific requirements for organotypic microtissues, spheroids and solid matrix cultures. We conclude on the current progress, potential, benefits and limitations of cell culture monitoring systems from monolayer culture to organ-on-chip systems.

Crosstalk between calcium and reactive oxygen species signaling in cancer

The interplay between Ca²⁺ and reactive oxygen species (ROS) signaling pathways is well established, with reciprocal regulation occurring at a number of subcellular locations. Many Ca²⁺ channels at the cell surface and intracellular organelles, including the endoplasmic reticulum and mitochondria are regulated by redox modifications. In turn, Ca²⁺ signaling can influence the cellular generation of ROS, from sources such as NADPH oxidases and mitochondria. This relationship has been explored in great depth during the process of apoptosis, where surges of Ca²⁺ and ROS are important mediators of cell death. More recently, coordinated and localized Ca²⁺ and ROS transients appear to play a major role in a vast variety of pro-survival signaling pathways that may be crucial for both physiological and pathophysiological functions. While much work is required to firmly establish this Ca²⁺-ROS relationship in cancer, existing evidence from other disease models suggests this crosstalk is likely of significant importance in tumorigenesis. In this review, we describe the regulation of Ca²⁺ channels and transporters by oxidants and discuss the potential consequences of the ROS-Ca²⁺ interplay in tumor cells.

Enhanced release of primary signals may render intercellular signalling ineffective due to spatial aspects

Detailed mechanistic modelling has been performed of the intercellular signalling cascade between precancerous cells and their normal neighbours that leads to a selective removal of the precancerous cells by apoptosis. Two interconnected signalling pathways that were identified experimentally have been modelled, explicitly accounting for temporal and spatial effects. The model predicts highly non-linear behaviour of the signalling. Importantly, under certain conditions, enhanced release of primary signals by precancerous cells renders the signalling ineffective. This counter-intuitive behaviour arises due to spatial aspects of the underlying signalling scheme: Increased primary signalling by precancerous cells does, upon reaction with factors derived from normal cells, produce higher yields of apoptosis-triggering molecules. However, the apoptosis-triggering signals are formed farther from the precancerous cells, so that these are attacked less efficiently. Spatial effects thus may represent a novel analogue of negative feedback mechanisms.

Reactive oxygen species: Reactions and detection from photosynthetic tissues

Reactive oxygen species (ROS) have long been recognized as compounds with dual roles. They cause cellular damage by reacting with biomolecules but they also function as agents of cellular signaling. Several different oxygen-containing compounds are classified as ROS because they react, at least with certain partners, more rapidly than ground-state molecular oxygen or because they are known to have biological effects. The present review describes the typical reactions of the most important ROS. The reactions are the basis for both the detection methods and for prediction of reactions between ROS and biomolecules. Chemical and physical methods used for detection, visualization and quantification of ROS from plants, algae and cyanobacteria will be reviewed. The main focus will be on photosynthetic tissues, and limitations of the methods will be discussed.

Impact of intercellular induction of apoptosis on low-dose radiation carcinogenesis

In vitro data indicate that selective removal of oncogenic transformed cells by apoptosis induced via signalling by neighbouring cells may represent an important anti-carcinogenic process. Mechanistic modelling supports this concept and predicts that the phenomenon can stop the growth of a transformed cell population, forming a dormant pre-neoplastic lesion, or even remove the transformed clone completely. Radiation has been shown to enhance the underpinning signalling and increase the extent and rate of apoptosis induction in precancerous cells. Implications for low-dose radiation carcinogenesis are discussed based on in vitro data and mechanistic modelling. The possibility is outlined for radiation to act in a pro-carcinogenic manner, i.e. to reduce rather than enhance the removal of transformed cells by apoptosis. The effects of radiation exposure during early or late carcinogenesis are discussed.

Glycosaminoglycan degradation by selected reactive oxygen species

SIGNIFICANCE

Inflammatory diseases (such as arthritis) of the extracellular matrix (ECM) are of considerable socioeconomic significance. There is clear evidence that reactive oxygen species (ROS) and nitrogen species released by, for instance, neutrophils contribute to the degradation of the ECM. Here we will focus on the ROS-induced degradation of the glycosaminoglycans, one important component of the ECM.

RECENT ADVANCES

The recently developed "anti-TNF-α" therapy is primarily directed against neutrophilic granulocytes that are powerful sources of ROS. Therefore, a more detailed look into the mechanisms of the reactions of these ROS is reasonable.

CRITICAL ISSUES

Since both enzymes and ROS contribute to the pathogenesis of inflammatory diseases, it is very difficult to estimate the contributions of the individual species in a complex biological environment. This particularly applies as many products are not stable but only transient products that decompose in a time-dependent manner. Thus, the development of suitable analytical methods as well as the establishment of useful biomarkers is a challenging aspect.

FUTURE DIRECTIONS

If the mechanisms of ECM destruction are understood in more detail, then the development of suitable drugs to treat inflammatory diseases will be hopefully much more successful.

Large-scale investigation of oxygen response mutants in Saccharomyces cerevisiae

A genome-wide screen of a yeast non-essential gene-deletion library was used to identify sick phenotypes due to oxygen deprivation. The screen provided a manageable list of 384 potentially novel as well as known oxygen responding (anoxia-survival) genes. The gene-deletion mutants were further assayed for sensitivity to ferrozine and cobalt to obtain a subset of 34 oxygen-responsive candidate genes including the known hypoxic gene activator, MGA2. With each mutant in this subset a plasmid based β-galactosidase assay was performed using the anoxic-inducible promoter from OLE1 gene, and 17 gene deletions were identified that inhibit induction under anaerobic conditions. Genetic interaction analysis for one of these mutants, the RNase-encoding POP2 gene, revealed synthetic sick interactions with a number of genes involved in oxygen sensing and response. Knockdown experiments for CNOT8, human homolog of POP2, reduced cell survival under low oxygen condition suggesting a similar function in human cells.

Mechanistic modelling suggests that the size of preneoplastic lesions is limited by intercellular induction of apoptosis in oncogenically transformed cells

Selective removal of oncogenically transformed cells by apoptosis induced via signalling by surrounding cells has been suggested to represent a natural anticarcinogenic process. To investigate its potential effect in detail, a mechanistic model of this process is proposed. The model is calibrated against in vitro data on apoptosis triggered in transformed cells by defined external inducers as well as through signalling by normal cells under coculture conditions. The model predicts that intercellular induction of apoptosis is capable of balancing the proliferation of oncogenically transformed cells and limiting the size of their populations over long times, even if their proliferation per se were unlimited. Experimental research is desired to verify whether the predicted stable population of transformed cells corresponds to a kind of dormancy during early-stage carcinogenesis (dormant preneoplastic lesions), and how this process relates to other anticarcinogenic mechanisms taking place under in vivo conditions.

Differential cysteine depletion in respiratory chain complexes enables the distinction of longevity from aerobicity

Mitochondrially encoded proteins in long-lived animals exhibit a characteristic anomaly on the amino acid usage level: they abstain from the use of cysteine in a lifespan-dependent fashion. Here, we have further investigated this phenomenon by analyzing respiratory chain complex subunits individually. We find that complex I cysteine depletion is the almost exclusive carrier of the cysteine-lifespan correlation, whereas complex IV cysteine depletion is uniform in all aerobic animals, unrelated to longevity, but even more pronounced than complex I cysteine depletion in the longest-lived species. In nuclear encoded subunits of the respiratory chain, we find lifespan-independent cysteine depletion ranging from moderate in complex I to severe in complex V. However, a separate analysis of the transmembrane domains of these proteins unmasks an intramembrane pattern of cysteine usage that significantly correlates with longevity. Hence, cysteine usage in the respiratory chain seems to be governed by two independent molecular mechanisms acting on the protein level: a global trend of cysteine avoidance in all proteins, and a specific effect on transmembrane domain cysteines that reflects longevity. To account for these characteristic patterns, a thiyl radical-based molecular mechanism of intramembrane hydrophobic cross-linking is discussed.

Modelling of intercellular induction of apoptosis in oncogenic transformed cells and radiation effects on the phenomenon

The removal of transformed cells via induction of apoptosis through intercellular signalling by surrounding cells is supposed to represent an important control mechanism limiting carcinogenesis. Low doses of radiation influence the efficiency of this anti-carcinogenesis process, indicating possible beneficial effects of low doses of radiation mediated by intercellular communication ('non-targeted effects'). To quantitatively understand the signalling system involved and the effects of radiation and to assess the role of this phenomenon in radiation-induced carcinogenesis, multi-scale modelling studies have been started. The proposed kinetic model takes into account (i) triggering of the effector function in cells in the vicinity of transformed cells, (ii) intercellular signalling between effector and transformed cells and (iii) execution of apoptosis in attacked cells. The systems model without radiation perturbance is reviewed. First results accounting for radiation-induced modulations of the signalling schemes are presented.

A revisit to O2 sensing and transduction in the carotid body chemoreceptors in the context of reactive oxygen species biology

Oxygen-sensing and transduction in purposeful responses in cells and organisms is of great physiological and medical interest. All animals, including humans, encounter in their lifespan many situations in which oxygen availability might be insufficient, whether acutely or chronically, physiologically or pathologically. Therefore to trace at the molecular level the sequence of events or steps connecting the oxygen deficit with the cell responses is of interest in itself as an achievement of science. In addition, it is also of great medical interest as such knowledge might facilitate the therapeutical approach to patients and to design strategies to minimize hypoxic damage. In our article we define the concepts of sensors and transducers, the steps of the hypoxic transduction cascade in the carotid body chemoreceptor cells and also discuss current models of oxygen- sensing (bioenergetic, biosynthetic and conformational) with their supportive and unsupportive data from updated literature. We envision oxygen-sensing in carotid body chemoreceptor cells as a process initiated at the level of plasma membrane and performed by a hemoprotein, which might be NOX4 or a hemoprotein not yet chemically identified. Upon oxygen-desaturation, the sensor would experience conformational changes allosterically transmitted to oxygen regulated K+ channels, the initial effectors in the transduction cascade. A decrease in their opening probability would produce cell depolarization, activation of voltage dependent calcium channels and release of neurotransmitters. Neurotransmitters would activate the nerve endings of the carotid body sensory nerve to convey the information of the hypoxic situation to the central nervous system that would command ventilation to fight hypoxia.

Mammalian mitochondrial complex I: biogenesis, regulation, and reactive oxygen species generation

Virtually every mammalian cell contains mitochondria. These double-membrane organelles continuously change shape and position and contain the complete metabolic machinery for the oxidative conversion of pyruvate, fatty acids, and amino acids into ATP. Mitochondria are crucially involved in cellular Ca2+ and redox homeostasis and apoptosis induction. Maintenance of mitochondrial function and integrity requires an inside-negative potential difference across the mitochondrial inner membrane. This potential is sustained by the electron-transport chain (ETC). NADH:ubiquinone oxidoreductase or complex I (CI), the first and largest protein complex of the ETC, couples the oxidation of NADH to the reduction of ubiquinone. During this process, electrons can escape from CI and react with ambient oxygen to produce superoxide and derived reactive oxygen species (ROS). Depending on the balance between their production and removal by antioxidant systems, ROS may function as signaling molecules or induce damage to a variety of biomolecules or both. The latter ultimately leads to a loss of mitochondrial and cellular function and integrity. In this review, we discuss (a) the role of CI in mitochondrial functioning; (b) the composition, structure, and biogenesis of CI; (c) regulation of CI function; (d) the role of CI in ROS generation; and (e) adaptive responses to CI deficiency.

NOX and inflammation in the vascular adventitia

Vascular inflammation has traditionally been thought to be initiated at the luminal surface and progress through the media toward the adventitial layer. In recent years, however, evidence has emerged suggesting that the vascular adventitia is activated early in a variety of cardiovascular diseases and that it plays an important role in the initiation and progression of vascular inflammation. Adventitial fibroblasts have been shown to produce substantial amounts of NAD(P)H oxidase-derived reactive oxygen species (ROS) in response to vascular injury. Additionally, inflammatory cytokines, lipids, and various hormones, implicated in fibroblast proliferation and migration, lead to recruitment of inflammatory cells to the adventitial layer and impairment of endothelium-dependent relaxation. Early in the development of vascular disease, there is clear evidence for progression toward a denser vasa vasorum which delivers oxygen and nutrients to an increasingly hypoxic and nutrient-deficient media. This expanded vascularization appears to provide enhanced delivery of inflammatory cells to the adventitia and outer media. Combined adventitial fibroblast and inflammatory cell-derived ROS therefore are expected to synergize their local effect on adventitial parenchymal cells, leading to further cytokine release and a feed-forward propagation of adventitial ROS production. In fact, data from our laboratory and others suggest a broader paracrine positive feedback role for adventitia-derived ROS in medial smooth muscle cell hypertrophy and neointimal hyperplasia. A likely candidate responsible for the adventitia-derived paracrine signaling across the vessel wall is the superoxide anion metabolite hydrogen peroxide, which is highly stable, cell permeant, and capable of activating downstream signaling mechanisms in smooth muscle cells, leading to phenotypic modulation of smooth muscle cells. This review addresses the role of adventitial NAD(P)H oxidase-derived ROS from a nontraditional, perivascular vantage of promoting vascular inflammation and will discuss how ROS derived from adventitial NAD(P)H oxidases may be a catalyst for vascular remodeling and dysfunction.

The proteasome and its role in the degradation of oxidized proteins

The generation of free radicals and the resulting oxidative modification of cell structures are omnipresent in mammalian cells. This includes the permanent oxidation of proteins leading to the disruption of the protein structure and an impaired functionality. In consequence, these oxidized proteins have to be removed in order to prevent serious metabolic disturbances. The most important cellular proteolytic system responsible for the removal of oxidized proteins is the proteasomal system. For normal functioning, the proteasomal system needs the coordinated interaction of numerous components. This review describes the fundamental functions of the 20S "core" proteasome, its regulators, and the roles of the proteasomal system beyond the removal of oxidized proteins in mammalian cells.

Role of oxidative stress and nitric oxide in atherothrombosis

During the last decade basic and clinical research has highlighted the central role of reactive oxygen species (ROS) in cardiovascular disease. Enhanced production or attenuated degradation of ROS leads to oxidative stress, a process that affects endothelial and vascular function, and contributes to vascular disease. Nitric oxide (NO), a product of the normal endothelium, is a principal determinant of normal endothelial and vascular function. In states of inflammation, NO production by the vasculature increases considerably and, in conjunction with other ROS, contributes to oxidative stress. This review examines the role of oxidative stress and NO in mechanisms of endothelial and vascular dysfunction with an emphasis on atherothrombosis.

Low dose radiation and intercellular induction of apoptosis: potential implications for the control of oncogenesis

PURPOSE

This review is focused on the potential impact of low dose radiation effects on intercellular induction of apoptosis and the underlying reactive-oxygen species (ROS)-mediated signaling pathways.

RESULTS

Transformed cells are subject to ROS-mediated apoptosis induction by non-transformed cells ('intercellular induction of apoptosis') and by ROS-mediated autocrine self-destruction. Sensitivity to intercellular induction of apoptosis and autocrine self-destruction are strictly correlated to the expression of the transformed state. Extracellular superoxide anions generated by transformed target cells drive the selectivity and sensitivity of this signaling system which is based on four different signaling pathways. Low dose irradiation of non-transformed cells enhances intercellular induction of apoptosis in transformed cells. This process is controlled by TGF-beta and seems to depend on the induction of peroxidase release. In addition, low dose radiation enhances superoxide anion generation of transformed target cells.

CONCLUSIONS

Low dose radiation-triggered enhancement of intercellular induction of apoptosis and autocrine self-destruction might represent a potential control system during carcinogenesis. It might be the underlying mechanism for the well-known inhibitory effect of low dose radiation on detectable transformation events. However, modifications of the complex intercellular ROS-based signaling system may also lead to configurations in which low dose radiation attenuates ROS-mediated apoptosis induction.

Extracellular superoxide dismutase and oxidant damage in osteoarthritis

OBJECTIVE

To use human cartilage samples and a mouse model of osteoarthritis (OA) to determine whether extracellular superoxide dismutase (EC-SOD) is a constituent of cartilage and to evaluate whether there is a relationship between EC-SOD deficiency and OA.

METHODS

Samples of human cartilage were obtained from femoral heads at the time of joint replacement surgery for OA or femoral neck fracture. Samples of mouse tibial cartilage obtained from STR/ort mice and CBA control mice were compared at 5, 15, and 35 weeks of age. EC-SOD was measured by enzyme-linked immunosorbent assay, Western blotting, and immunohistochemistry techniques. Real-time quantitative reverse transcription-polymerase chain reaction was used to measure messenger RNA for EC-SOD and for endothelial cell, neuronal, and inducible nitric oxide synthases. Nitrotyrosine formation was assayed by Western blotting in mouse cartilage and by fluorescence immunohistochemistry in human cartilage.

RESULTS

Human articular cartilage contained large amounts of EC-SOD (mean +/- SEM 18.8 +/- 3.8 ng/gm wet weight of cartilage). Cartilage from patients with OA had an approximately 4-fold lower level of EC-SOD compared with cartilage from patients with hip fracture. Young STR/ort mice had decreased levels of EC-SOD in tibial cartilage before histologic evidence of disease occurred, as well as significantly more nitrotyrosine formation at all ages studied.

CONCLUSION

EC-SOD, the major scavenger of reactive oxygen species in extracellular spaces, is decreased in humans with OA and in an animal model of OA. Our findings suggest that inadequate control of reactive oxygen species plays a role in the pathophysiology of OA.

Bystander signaling between glioma cells and fibroblasts targeted with counted particles

Radiation-induced bystander effects may play an important role in cancer risks associated with environmental, occupational and medical exposures and they may also present a therapeutic opportunity to modulate the efficacy of radiotherapy. However, the mechanisms underpinning these responses between tumor and normal cells are poorly understood. Using a microbeam, we investigated interactions between T98G malignant glioma cells and AG01522 normal fibroblasts by targeting cells through their nuclei in one population, then detecting cellular responses in the other co-cultured non-irradiated population. It was found that when a fraction of cells was individually irradiated with exactly 1 or 5 helium particles ((3)He(2+)), the yield of micronuclei (MN) in the non-irradiated population was significantly increased. This increase was not related to the fraction of cells targeted or the number of particles delivered to those cells. Even when one cell was targeted with a single (3)He(2+), the induction of MN in the bystander non-irradiated population could be increased by 79% for AG01522 and 28% for T98G. Furthermore, studies showed that nitric oxide (NO) and reactive oxygen species (ROS) were involved in these bystander responses. Following nuclear irradiation in only 1% of cells, the NO level in the T98G population was increased by 31% and the ROS level in the AG0 population was increased by 18%. Treatment of cultures with 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (c-PTIO), an NO scavenger, abolished the bystander MN induction in non-irradiated AG01522 cells but only partially in non-irradiated T98G cells, and this could be eliminated by treatment with either DMSO or antioxidants. Our findings indicate that differential mechanisms involving NO and ROS signaling factors play a role in bystander responses generated from targeted T98G glioma and AG0 fibroblasts, respectively. These bystander interactions suggest that a mechanistic control of the bystander effect could be of benefit to radiotherapy.

Inhibitory Effects of Metabolite I of Erdosteine on the Generation of Nitric Oxide and Peroxynitrite Chemiluminescence by Human Neutrophils

Polymorphonuclear neutrophils (PMNs) can generate superoxide anions and nitric oxide (NO), which is not only an important mediator of various cellular activities, but can also react with superoxide anions to produce peroxynitrite anions (ONOO-). Peroxynitrite is a potent and potentially toxic oxidant that damages various types of biomolecules. It preferentially mediates the oxidation of thiolic groups in protein and non-protein molecules, thus altering their functions. The aim of this study was to examine whether, in addition to its ability to reduce the respiratory bursts of human PMNs, the SH metabolite I (Met I) of erdosteine, can interfere with NO and NO-derived peroxynitrite production, thus extending its antioxidant activity. This was done by means of the luminol amplified chemiluminescence (LACL), which has been widely used to detect the production of reactive oxidant species (ROS) by PMNs under various conditions. At 5 and 10 microg/ml, Met I significantly reduced LACL after fMLP and PMA stimulation. When L-Arg was added to the reaction medium, as a NO donor, the chemiluminescence of fMLP increased by up to 67% and that of PMA by up to 132%, but was once again significantly reduced by 5 and 10 microg/ml of Met I. In a cell-free system, the use of linsidomine (SIN-1) makes it possible to investigate the behavior of LACL induced by peroxynitrite release, which was significantly reduced by Met I concentrations ranging from 1.25 to 10 microg/ml. Our findings indicate that Met I, a molecule with a SH group, reacts with ROS, NO and NO-derived peroxynitrite, and has both antioxidant and scavenging activity. This is of interest for the strategy of protecting against damage induced by radical species in the pulmonary cell environment, in which they can induce a phlogogenic loop, and suggests that adding exogenous thiols may be useful in antagonizing the toxic effects of reactive molecules on endogenous thiols.

Angiotensin II-NAD(P)H oxidase-stimulated superoxide modifies tubulovascular nitric oxide cross-talk in renal outer medulla

The source of superoxide (O2*-) production and cell-to-cell interactions of O2*- and nitric oxide (NO) in response to angiotensin II (AngII) were studied by fluorescence microscopic techniques to image rat renal outer medullary microtissue strips. Changes in intracellular O2*- were determined by dihydroethidium-ethidium ratios, and NO was determined with 4,5-diaminofluorescein diacetate. AngII (1 micromol/L) significantly increased O2*- in the isolated, medullary thick ascending limb (mTAL). These responses were inhibited by the superoxide dismutase mimetic 4-hydroxytetramethylpiperidine-1-oxyl (TEMPOL) and by the NAD(P)H oxidase inhibitors diphenylene iodonium and apocynin. AngII did not increase O2*- in either pericytes of isolated, intact vasa recta (VR) or pericytes of VR with a disrupted endothelium, even when surrounded by mTAL. However, AngII did increase O2*- when the tissue strips were preincubated with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), indicating that cross-talk of O2*- from mTAL to the VR occurred but was normally inhibited by NO. Also, tissue O2*- reduction by TEMPOL increased the diffusion of NO from mTAL to the pericytes, indicating that cross-talk of NO from the mTAL to the VR is also inhibited by O2*-. We conclude that AngII stimulates O2*- production in mTAL via the NAD(P)H oxidase pathway and that interactions of O2*- and NO ultimately determine the effectiveness of in situ free-radical cross-talk between the mTAL and the VR.

Synergistic enhancement of H2O2 production in human epidermoid carcinoma cells by Benzo[a]pyrene and ultraviolet A radiation

Benzo[a]pyrene (BaP) is an ubiquitous environmental pollutant with potential carcinogenecity. It was shown that BaP, upon irradiation by UV A, enhanced the formation of 8-hydroxy-2'-deoxyguanosine in purified DNA and in cultured cells. The purpose of this present study was to determine whether BaP and UV radiation synergistically generate reactive oxygen species (ROS) that consequently result in the oxidation of DNA bases. In this study, the levels of H(2)O(2) were measured as an indicator of ROS in A431 cells and primary human keratinocytes treated with BaP plus UV radiation. Production of H(2)O(2) significantly increased from cells treated with BaP plus UVB or UVA, with the latter having a much greater effect. The responses of A431 cells and primary human keratinocytes to BaP and UVA irradiation were similar in generation of extracellular H(2)O(2). Also, H(2)O(2) production proportionally correlated with UVA and UVB dose, but was independent of time or BaP concentration. Treatment with catalase and general ROS scavengers significantly decreased H(2)O(2) production from cells treated with BaP plus UVA, whereas scavengers of *O2-, *OH, and (1)O(2) had minimal effects. These results demonstrate that BaP synergistically enhances the production of H(2)O(2) from cultured cells by UVA and, to a lesser extent, by UVB, supporting the hypothesis that interaction of BaP and UVA can generate ROS and further substantiate oxidative DNA damage that may lead to carcinogenesis.

Proapoptotic and redox state-related signaling of reactive oxygen species generated by transformed fibroblasts

Oncogenic transformed fibroblasts are characterized by extracellular superoxide anion generation through a membrane-associated NADPH oxidase. After cellular glutathione depletion, extracellular reactive oxygen species (ROS) generated by transformed fibroblasts exhibit a strong apoptosis-inducing potential. As apoptosis induction under glutathione depletion is inhibited by catalase, the NADPH oxidase inhibitor apocynin, superoxide dismutase, the hydroxyl radical scavenger terephthalate and the iron chelator deferoxamine, the metal-catalysed Haber-Weiss reaction seems to be the responsible signaling mechanism. In contrast to extracellular ROS, intracellular ROS play no role for apoptosis induction in glutathione-depleted transformed fibroblasts initially, since a high level of intracellular catalase scavenges intracellular hydrogen peroxide. Intracellular catalase seems to be induced by extracellular hydrogen peroxide, as pretreatment of transformed fibroblasts with exogenous catalase downmodulates endogenous catalase and renders glutathione-depleted transformed cells susceptible for the effect of endogenous hydrogen peroxide. In contrast to transformed fibroblasts, nontransformed glutathione-depleted fibroblasts do not generate substantial extracellular ROS, but apoptosis is efficiently induced in these cells by intracellular ROS. Our data show that extracellular ROS of transformed fibroblasts exhibit redox-related signaling and at the same time represent a potential apoptosis-inducing hazard through the metal-catalysed Haber-Weiss reaction.

Genotoxicity associated with NO production in macrophages and co-cultured target cells

We previously used mouse macrophage-like RAW264.7 cells as an experimental system for the study of nitric oxide (NO)-associated genotoxicity under physiologically relevant conditions, and characterized genotoxic effects in the NO-producing cells. Here we report experiments utilizing a co-culture system enabling parallel studies of cytotoxic and genotoxic responses in co-cultured target cells as well as in macrophages stimulated to produce NO. We found that co-cultivation with macrophages stimulated to produce NO for 38-42 h resulted in significant increases in mutant fraction in the endogenous genes of target human TK6 and hamster CHO-AA8 cells and in the macrophages themselves, accompanied by a substantial decrease in cell viability. Addition of N-methyl-L-arginine, an NO synthase inhibitor, abrogated much of the cytotoxicity and genotoxicity in both target and macrophages cells, verifying the role of NO in the induction of these responses. We also showed that NO-associated genotoxic response in macrophages could be influenced by culture medium. Collectively, these results support the hypothesis that NO production by activated macrophages may contribute to genotoxic risks associated with chronic inflammation.

Nitric oxide mediates apoptosis induction selectively in transformed fibroblasts compared to nontransformed fibroblasts

Nitric oxide (NO) mediates apoptosis induction in fibroblasts with constitutive src or induced ras oncogene expression, whereas nontransformed parental cells and revertants are not affected. This direct link between the transformed phenotype and sensitivity to NO-mediated apoptosis induction seems to be based on the recently described extracellular superoxide anion generation by transformed cells, as NO-mediated apoptosis induction in transformed cells is inhibited by extracellular superoxide dismutase (SOD), by SOD mimetics and by apocynin, an inhibitor of NADPH oxidase. Furthermore, nonresponsive nontransformed cells can be rendered sensitive for NO-mediated apoptosis induction when they are supplemented with xanthine oxidase/xanthine as an extracellular source for superoxide anions. As superoxide anions and NO readily interact in a diffusion-controlled reaction to generate peroxynitrite, peroxynitrite seems to be the responsible apoptosis inducer in NO-mediated apoptosis induction. In line with this conclusion, NO-mediated apoptosis induction in superoxide anion-generating transformed cells is inhibited by the peroxynitrite scavengers ebselen and FeTPPS. Moreover, direct application of peroxynitrite induces apoptosis both in transformed and nontransformed cells, indicating that peroxynitrite is no selective apoptosis inducer per se, but that selective apoptosis induction in transformed cells by NO is achieved through selective peroxynitrite generation. The interaction of NO with target cell derived superoxide anions represents a novel concept for selective apoptosis induction in transformed cells. This mechanism may be the basis for selective apoptosis induction by natural antitumor systems (like macrophages, natural killer cells, granulocytes) that utilize NO for antitumor action. Apoptosis induction mediated by NO involves mitochondrial depolarization and is blocked by Bcl-2 overexpression.

Peroxynitrite-mediated stress is associated with proliferation of human metastatic colorectal carcinoma in the liver

3-Nitrotyrosine (3-NT), a product of peroxynitrite reaction, is abundantly observed in hepatocytes adjacent to human metastatic colorectal carcinoma. To elucidate its biological significance, we undertook to identify nitric oxide (NO)-producing cells and apoptosis under oxidative stress. We observed strong inducible NO-synthase (iNOS) immunoreactivity in the hepatocytes adjacent to metastatic tumor, revealing an identical pattern to 3-NT immunostaining. Furthermore, intense 3-NT immunostaining of hepatocytes was associated with apoptosis whereas carcinoma cells near those hepatocytes presented high proliferating-cell nuclear antigen. Our results suggest that contact of metastatic tumor induces apoptosis in adjacent hepatocytes through peroxynitrite, thus permitting the proliferation of cancer cells.

An alternative signaling pathway based on nitryl chloride during intercellular induction of apoptosis

Transforming growth factor (TGF)-beta pretreated nontransformed fibroblasts induce apoptosis selectively in transformed fibroblasts. This potential control step during oncogenesis has been termed intercellular induction of apoptosis. Selectivity and efficiency of intercellular induction of apoptosis depend on transformed target cell-derived superoxide anions that drive two intercellular signaling pathways--the HOCl/hydroxyl radical and the nitric oxide (NO)/peroxynitrite pathway. Other natural antitumor systems like macrophages or cells of the granulocyte lineage seem to utilize the same signaling chemistry. Our data demonstrate the existence of an alternative signaling pathway in these systems. This pathway depends on the presence of nitrite and is still effective when the two conventional signaling pathways are blocked by superoxide dismutase (SOD). Nitrite-dependent apoptosis induction is neither blocked by SOD nor by the hydroxyl radical scavenger terephthalate, but it is inhibited by the peroxidase inhibitor aminobenzoyl hydrazide and by the hypochlorous acid (HOCl) scavenger taurine. Therefore, nitrite, that is nontoxic for our cells, seems to interact with HOCl to form the apoptosis inducer nitryl chloride. Nitryl chloride-mediated apoptosis induction might be relevant for apoptosis induction in tumor cells that release SOD and thus escape the two classical signaling pathways.

Signaling and proapoptotic functions of transformed cell-derived reactive oxygen species

Transformed fibroblasts generate extracellular superoxide anions through the recently identified membrane-associated NADPH oxidase. These cell-derived superoxide anions exhibit signaling functions such as regulation of proliferation and maintenance of the transformed state. Their dismutation product hydrogen peroxide regulates the intracellular level of catalase, whose activity has been observed to be upregulated in certain transformed cells. After glutathione depletion, transformed cell-derived reactive oxygen species (ROS) exhibit apoptosis-inducing potential through the metal-catalyzed Haber-Weiss reaction. Moreover, transformed cell-derived ROS represent key elements for selective and efficient apoptosis induction by natural antitumor systems (such as fibroblasts, granulocytes and macrophages). These effector cells release peroxidase, which utilizes target cell-derived hydrogen peroxide for HOCl synthesis. In a second step, HOCl interacts with target cell-derived superoxide anions and forms apoptosis-inducing hydroxyl radicals. In a parallel signaling pathway, effector cell-derived NO interacts with target cell-derived superoxide anions and generates the apoptosis inducer peroxynitrite. Therefore, transformed cell-derived ROS determine transformed cells as selective targets for induction of apoptosis by these effector systems. It is therefore proposed that transformed cell derived ROS interact with associated cells to exhibit directed and specific signaling functions, some of which are beneficial and some of which can become detrimental to transformed cells.

Lactobacilli-mediated control of vaginal cancer through specific reactive oxygen species interaction

Klebanoff et al. proposed that hydrogen peroxide-producing lactobacilli and peroxidase in the vagina of healthy women might be responsible for the prevention of vaginosis and also might exert an antitumor effect (1). Based on recent evidence on superoxide anion generation by transformed cells (2,3) and on the potential of myeloperoxidase for selective apoptosis induction in transformed cells (4), a model for specific reactive oxygen species interaction during lactobacilli-mediated tumor control in the vagina is presented here. We propose that peroxidase, which converts hydrogen peroxide into hypochlorous acid, is responsible for creating a microbicidal vaginal milieu by maintaining a balanced, non-toxic, steady state level of the microbicides H(2)O(2)and HOCI. In case individual superoxide anion-producing transformed cells eventually appear in the mucosa they will be driven into apoptosis by interaction of HOCI with superoxide anions which leads to the generation of hydroxyl radicals. Hence selective apoptosis induction in transformed cells represents the key element of lactobacilli-mediated antitumor defense. Since papilloma virus infected cells are resistant to this pathway of apoptosis induction, they are plausible candidates for circumvention of lactobacilli-mediated control of oncogenesis.

Transformed target cell-derived superoxide anions drive apoptosis induction by myeloperoxidase

Myeloperoxidase induces apoptosis in src- or raxs-transformed fibroblasts, but not in parental nontransformed fibroblasts. This selectivity seems to be based on superoxide anion production by transformed cells, a recently described characteristic feature of transformed cells. Myeloperoxidase-mediated apoptosis induction is inhibited by SOD, catalase, 4-aminobenzoyl hydrazide, taurine and DMSO. This pattern of inhibition allows us to conclude that transformed cell derived superoxide anions dismutate to hydrogen peroxide, which fosters HOCl formation by myeloperoxidase. Hydrogen peroxide formation thereby is the rate-limiting step and depends on the cell density. In a second step, HOCl interacts with superoxide anions to yield the highly reactive apoptosis inducing hydroxyl radical. This conclusion was verified through selective apoptosis induction in transformed cells by direct addition of HOCl, which was also inhibited by SOD and DMSO. Our findings demonstrate a specific interplay between target cell derived superoxide anions and MPO during selective apoptosis induction.

Target cell-derived superoxide anions cause efficiency and selectivity of intercellular induction of apoptosis

Transformed fibroblasts are specifically eliminated by their nontransformed neighbors through intercellular induction of apoptosis. This process depends on the number of nontransformed effector cells and on the local density of transformed target cells. Intercellular signalling is inhibited by SOD (a scavenger of superoxide anions), taurine (a scavenger of HOCl), 4-aminobenzoyl hydrazide (a mechanism-based inhibitor of peroxidase), DMSO (a hydroxyl radical scavenger), and two inhibitors of NO synthase. Therefore, selective apoptosis induction seems to be based on superoxide anion production by transformed cells, their spontaneous dismutation to hydrogen peroxide, and HOCl generation by a novel effector cell-derived peroxidase. HOCl then interacts with target cell-derived superoxide anions to yield hydroxyl radicals. Due to the short diffusion pathway of superoxide anions, hydroxyl radical generation is confined to the intimate vicinity of transformed cells. In parallel, NO derived from effector cells interacts with superoxide anions of target cells to yield the apoptosis inducer peroxynitrite. Reconstitution experiments using transformed or nontransformed cells in conjunction with myeloperoxidase, HOCl, or an NO donor demonstrated that superoxide anions generated extracellularly by transformed cells participate in intercellular signalling and at the same time determine transformed cells as selective targets for intercellular induction of apoptosis.

Superoxide release from interleukin-1B-stimulated human vascular cells: in situ electrochemical measurement

Release of superoxide anion by cultured vascular cells was investigated with the use of selective microelectrodes. Local concentration of superoxide anion (O2*-) was followed by differential pulse amperometry on a carbon microfiber at 0.1 V/SCE. The oxidation current allows O2*- detection in the 10(-8) M concentration range without interference of the other major oxygen species. Interleukin-1beta-stimulated O2*- release that progressively increased to reach local concentrations at the cell membrane level of 76 +/- 11 nm 40-60 min after stimulation in human cord vein endothelial cells, and 131 +/- 18 nm 1-2 h after stimulation in internal mammary artery smooth muscle cells. In the two types of cells, the O2*- oxidation signal was suppressed in the presence of superoxide dismutase. Spontaneous O2*-release from unstimulated cells was undetectable. These results demonstrate that selective microelectrodes allow direct and real-time monitoring of local O2*- released from vascular endothelial as well as from smooth muscle cells submitted to an inflammatory stimulus.

Keratinocyte superoxide generation

We have demonstrated using the reduction of cytochrome c, that the keratinocyte cell line H357 generates superoxide at significant rates (8.36 nmol/h/10[6] cells). The rate of superoxide release decreased as the cells reached confluence. Superoxide production was increased more than twofold following preincubation with IL-1beta, or by the addition of the Ca2+ ionophore, Ionomycin. Other stimuli known to activate the NADPH oxidase of phagocytes were ineffective, but the regulatory cytokine IFNgamma lowered the rate of release. Inhibitors of lipoxygenase function decreased the rate of superoxide production, whereas inhibitors of cyclo-oxygenase, xanthine oxidase, or NADPH oxidase failed to inhibit. The addition of NADH or NADPH to whole cells increased the rate threefold.

Seasonal variation in the antioxidant defense system of the brain of the ground squirrel (Citellus citellus) and response to low temperature compared with rat

Seasonal variation in the activity of antioxidant enzymes (superoxide dismutase (EC 1.15.1.1.; SOD), catalase (EC 1.11.1.6; CAT), glutathione peroxidase (EC 1.11.1.9; GSH-Px), glutathione reductase (EC 1.6.4.2; GR), glutathione-S-transferase (EC 2.5.1.18; GST) and low-molecular-weight antioxidants: ascorbic acid (AsA), vitamin E (VIT E) and glutathione (CSH+GSSG) were examined in the brain of the ground squirrels (Citellus citellus) maintained at 30 degrees C during the whole year. The highest activity (per mg protein) of antioxidant defense (AD) enzymes was found in the spring and was much lower in the summer. A further decrease in activity of CAT, GSH-Px and GST was observed in the winter. The highest levels of AsA and glutathione were recorded in winter in comparison with spring and summer. AD system in the brain of the ground squirrel and rates (maintained at thermoneutrality) exposed to low temperature (4 degrees C) for 3, 6 or 24 hr during the summer was studied as well. Summer was chosen as a period of stable euthermia for ground squirrels and in thermoregulation similar to rats. Consumption of free fatty acid and glucose during the acute exposure to low temperature was found to be species specific. In the ground squirrel, an increase in the specific activities of SOD, after 3, 6 and 24 hr, CAT after 3 and 6 hr and GR after 6 hr of exposure to low temperature was detected. When activities were expressed in U/g wet mass, an increase of SOD after 3, 6 and 24 hr (P < 0.02, P < 0.02, P < 0.005) and CAT and GSH-Px 3 hr (P < 0.01) upon exposure to low temperature was observed. In the rats, no changes in the specific activities of these enzymes after exposure to low temperature were recorded and only an increase in GST activity (U/g wet mass) after 6 hr exposure was registered. Low-molecular-weight AD components in both animal species were unchanged upon short-term exposure to low temperature. The species-specific differences in brain AD between the rats and the ground squirrels after short exposure to low temperature may be ascribed to seasonal changes of the brain activity in the latter.

Peroxynitrite: a two-faced metabolite of nitric oxide

The discovery that nitric oxide (NO) reacts with superoxide (O2.-) forming peroxynitrite (ONOO-) (1) and the proof that this reaction occurs in vivo (2,3) holds enormous implications for the understanding of free radicals in biological systems. Not only in mammalian defense mechanisms against microorganisms, but also in pathophysiology during overexposure of tissues to radicals or other highly reactive species. Peroxynitrite is a highly reactive compound with harmful effects on cells and could therefore be an important microbicidal compound. Furthermore, the reaction of superoxide with NO interferes with NO signalling mechanisms. NO is not only released in response to inflammatory agents by inflammatory cells, but is also an important messenger molecule in paracrine mechanisms and neurotransmission. Whether peroxynitrite formation is a negative side effect of NO and superoxide release, or a functional characteristic is yet to be determined, and will be discussed in this review.

Measurement of nitric oxide and peroxynitrite generation in the postischemic heart. Evidence for peroxynitrite-mediated reperfusion injury

Altered nitric oxide (NO.) production is a critical factor in tissue reperfusion injury; however, controversy remains regarding these alterations and how they cause injury. Since superoxide (O-2) generation is triggered during the early period of reperfusion the cytotoxic oxidant peroxynitrite (ONOO-) could be formed, but it is not known if this occurs. Therefore electron paramagnetic resonance and chemiluminescence studies were performed of the magnitude and time course of NO., O-2, and ONOO- formation in the postischemic heart. Isolated rat hearts were subjected either to normal perfusion or to reperfusion after 30 min of ischemia in the presence of the NO. trap Fe2+-N-methyl-D-glucamine dithiocarbamate with electron paramagnetic resonance measurements performed on the effluent. Although only trace signals were present prior to ischemia, prominent NO. adduct signals were seen during the first 2 min of reflow which were abolished by nitric oxide synthase (NOS) inhibition. Similar studies with the O-2 trap 5, 5-dimethyl-1-pyrroline N-oxide demonstrated a burst of O-2 generation over the first 2 min of reflow. Chemiluminescence measurements using 5-amino-2,3-dihydro-1,4-phthalazinedione (luminol) demonstrated a similar marked increase in ONOO- which was blocked by NOS inhibitors or superoxide dismutase. NOS inhibition or superoxide dismutase greatly enhanced the recovery of contractile function in postischemic hearts. Immunohistology demonstrated that the ONOO--mediated nitration product nitrotyrosine was formed in postischemic hearts but not in normally perfused controls. Thus, NO. formation is increased during the early period of reflow and reacts with O-2 to form ONOO-, which results in amino acid nitration and cellular injury.