Sensing and signalling in response to oxygen deprivation in plants and other organisms

AIMS AND SCOPE

All aerobic organisms require molecular di-oxygen (O2) for efficient production of ATP though oxidative phosphorylation. Cellular depletion of oxygen results in rapid molecular and physiological acclimation. The purpose of this review is to consider the processes of low oxygen sensing and response in diverse organisms, with special consideration of plant cells.

CONCLUSIONS

The sensing of oxygen deprivation in bacteria, fungi, metazoa and plants involves multiple sensors and signal transduction pathways. Cellular responses result in a reprogramming of gene expression and metabolic processes that enhance transient survival and can enable long-term tolerance to sub-optimal oxygen levels. The mechanism of sensing can involve molecules that directly bind or react with oxygen (direct sensing), or recognition of altered cellular homeostasis (indirect sensing). The growing knowledge of the activation of genes in response to oxygen deprivation has provided additional information on the response and acclimation processes. Conservation of calcium fluxes and reactive oxygen species as second messengers in signal transduction pathways in metazoa and plants may reflect the elemental importance of rapid sensing of cellular restriction in oxygen by aerobic organisms.

Seasonal variations in air pollution particle-induced inflammatory mediator release and oxidative stress

Health effects associated with particulate matter (PM) show seasonal variations. We hypothesized that these heterogeneous effects may be attributed partly to the differences in the elemental composition of PM. Normal human bronchial epithelial (NHBE) cells and alveolar macrophages (AMs) were exposed to equal mass of coarse [PM with aerodynamic diameter of 2.5-10 microm (PM(2.5-10)], fine (PM(2.5)), and ultrafine (PM(<0.1)) ambient PM from Chapel Hill, North Carolina, during October 2001 (fall) and January (winter), April (spring), and July (summer) 2002. Production of interleukin (IL)-8, IL-6, and reactive oxygen species (ROS) was measured. Coarse PM was more potent in inducing cytokines, but not ROSs, than was fine or ultrafine PM. In AMs, the October coarse PM was the most potent stimulator for IL-6 release, whereas the July PM consistently stimulated the highest ROS production measured by dichlorofluorescein acetate and dihydrorhodamine 123 (DHR). In NHBE cells, the January and the October PM were consistently the strongest stimulators for IL-8 and ROS, respectively. The July PM increased only ROS measured by DHR. PM had minimal effects on chemiluminescence. Principal-component analysis on elemental constituents of PM of all size fractions identified two factors, Cr/Al/Si/Ti/Fe/Cu and Zn/As/V/Ni/Pb/Se, with only the first factor correlating with IL-6/IL-8 release. Among the elements in the first factor, Fe and Si correlated with IL-6 release, whereas Cr correlated with IL-8 release. These positive correlations were confirmed in additional experiments with PM from all 12 months. These results indicate that elemental constituents of PM may in part account for the seasonal variations in PM-induced adverse health effects related to lung inflammation.

Characterization of a novel NADP(+)-dependent D-arabitol dehydrogenase from the plant pathogen Uromyces fabae

We have identified and characterized a novel NADP(+)-dependent D-arabitol dehydrogenase and the corresponding gene from the rust fungus Uromyces fabae, a biotrophic plant pathogen on broad bean (Vicia faba). The new enzyme was termed ARD1p (D-arabitol dehydrogenase 1). It recognizes D-arabitol and mannitol as substrates in the forward reaction, and D-xylulose, D-ribulose and D-fructose as substrates in the reverse reaction. Co-factor specificity was restricted to NADP(H). Kinetic data for the major substrates and co-factors are presented. A detailed analysis of the organization and expression pattern of the ARD1 gene are also given. Immunocytological data indicate a localization of the gene product predominantly in haustoria, the feeding structures of these fungi. Analyses of metabolite levels during pathogenesis indicate that the D-arabitol concentration rises dramatically as infection progresses, and D-arabitol was shown in an in vitro system to be capable of quenching reactive oxygen species involved in host plant defence reactions. ARD1p may therefore play an important role in carbohydrate metabolism and in establishing and/or maintaining the biotrophic interaction in U. fabae.

Development of an in vitro model of excess intracellular reactive oxygen species

These investigations characterize an in vitro model for generating excess intracellular reactive oxygen species (ROS). This novel model may be useful in the identification and delineation of cellular mechanisms associated with aging due to the link between age and excess oxidative events. The human cell line, MCF7, was stably transfected using the pSV3.neo plasmid housing a gene encoding the Aequorea victoria green fluorescent protein (GFP). Transfected cells were analyzed for maintenance of GFP over time, showing stability of the GFP gene. These studies demonstrate that the presence of fluorescing GFP significantly increases intracellular ROS, creating oxidative stress in these cells. Antioxidant supplementation was evaluated to determine the effectiveness of intracellular H2O2 reduction. The results demonstrate that supplementation with a potent antioxidant, such as reduced glutathione, protects cells from oxidative damage by decreasing intracellular concentrations of H2O2. This model for intracellular generation of excess ROS establishes a clear method by which the utility of antioxidant supplementation to protect against intracellularly generated reactive oxygen species may be evaluated.

Mitochondrial dysfunction resulting from loss of cytochrome c impairs cellular oxygen sensing and hypoxic HIF-alpha activation

While cellular responses to low oxygen (O(2)) or hypoxia have been studied extensively, the precise identity of mammalian cellular O(2) sensors remains controversial. Using murine embryonic cells lacking cytochrome c, and therefore mitochondrial activity, we show that mitochondrial reactive oxygen species (mtROS) are essential for proper O(2) sensing and subsequent HIF-1 alpha and HIF-2 alpha stabilization at 1.5% O(2). In the absence of this signal, HIF-alpha subunits continue to be degraded. Furthermore, exogenous treatment with H(2)O(2) or severe O(2) deprivation is sufficient to stabilize HIF-alpha even in the absence of cytochrome c and functional mitochondria. These results provide genetic evidence indicating that mtROS act upstream of prolyl hydroxylases in regulating HIF-1 alpha and HIF-2 alpha in this O(2)-sensing pathway.

Fluorescence in situ hybridisation analysis of chromosomal aberrations in gastric tissue: the potential involvement of Helicobacter pylori

In this series of experiments, a novel protocol was developed whereby gastric cells were collected using endoscopic cytology brush techniques, and prepared, such that interphase fluorescence in situ hybridization (FISH) could be performed. In total, 80 distinct histological samples from 37 patients were studied using four chromosome probes (over 32,000 cells analysed). Studies have previously identified abnormalities of these four chromosomes in upper GI tumours. Using premalignant tissues, we aimed to determine how early in Correa's pathway to gastric cancer these chromosome abnormalities occurred. Aneuploidy of chromosomes 4, 8, 20 and 17(p53) was detected in histologically normal gastric mucosa, as well as in gastritis, intestinal metaplasia, dysplasia and cancer samples. The levels of aneuploidy increased as disease severity increased. Amplification of chromosome 4 and chromosome 20, and deletion of chromosome 17(p53) were the more common findings. Hence, a role for these abnormalities may exist in the initiation of, and the progression to, gastric cancer. Helicobacter pylori infection was determined in premalignant tissue using histological analysis and PCR technology. Detection rates were comparable. PCR was used to subtype H. pylori for CagA status. The amplification of chromosome 4 in gastric tissue was significantly more prevalent in H. pylori-positive patients (n=7) compared to H. pylori-negative patients (n=11), possibly reflecting a role for chromosome 4 amplification in H. pylori-induced gastric cancer. The more virulent CagA strain of H. pylori was associated with increased disease pathology and chromosomal abnormalities, although numbers were small (CagA+ n=3, CagA- n=4). Finally, in vitro work demonstrated that the aneuploidy induced in a human cell line after exposure to the reactive oxygen species (ROS) hydrogen peroxide was similar to that already shown in the gastric cancer pathway, and may further strengthen the hypothesis that H. pylori causes gastric cancer progression via an ROS-mediated mechanism.

Avian uncoupling protein expressed in yeast mitochondria prevents endogenous free radical damage

The longevity of birds is surprising since they exhibit high metabolic rates and elevated blood sugar levels compared with mammals of the same body size, which presumably expose them to higher rates of free oxygen radical production, which is implicated in accelerated senescence. Uncoupling proteins (UCPs) are transporters of the inner mitochondrial membrane and their physiological activity is still a subject of debate. Avian UCP was found in birds but data on its activity are scarce. Avian UCP (Gallus gallus) was overexpressed in yeast and we assessed its ability to prevent mitochondrial reactive oxygen species (ROS) production by measuring ROS damage (aconitase activity) and antioxidant defences (MnSOD activity). We show that avian UCP protects yeast mitochondria against the deleterious impact of ROS, but without stimulation of superoxide dismutase activity. Avian UCP protein was specifically immunodetected and retinoic acid, which belongs to the carotenoid family, was found to trigger its activity. These data show that avian UCP basal activity protects against ROS damage. However, when activated by retinoic acid, avian UCP can also operate as the mammalian thermogenic UCP1. The hypothesis that avian UCP activities are state- and species-dependent is further discussed.

Hydrogen peroxide generated extracellularly by receptor-ligand interaction facilitates cell signaling

Reactive oxygen species (ROS) are key components of postreceptor intracellular signaling pathways; however, the role of ROS in signal initiation is uncertain. We discovered that receptor-ligand interaction caused the generation of hydrogen peroxide (H2O2). Using members of the hematopoietin receptor superfamily, as well as EGF receptor, we show that H2O2 is generated by specific receptor-ligand interaction in cells and in cell-free systems. With cognate ligand, the extracellular domain of the receptor was sufficient for H2O2 generation. We also found that production of H2O2 was diminished in a granulocyte-macrophage colony-stimulating factor receptor mutant unable to bind ligand. Exogenously added H2O2 induced signaling in the absence of ligand, whereas catalase and a membrane-bound peroxiredoxin inhibited ligand-dependent signaling. Our results suggest that H2O2 produced by receptor-ligand interaction is involved as a chemical mediator that facilitates cell signaling.

The induction of vascular endothelial growth factor by ultrafine carbon black contributes to the increase of alveolar-capillary permeability

Ultrafine carbon black (ufCB) can cause proinflammatory response and increase alveolar-capillary permeability. However, the mechanism underlying the increased permeability is not well characterized. Vascular endothelial growth factor (VEGF) is originally recognized as a vascular permeability factor. Oxidative stress generated by hydrogen peroxide (H2O2) stimulates VEGF gene expression. The purpose of this study was to explore the role of VEGF in ufCB-induced alveolar-capillary permeability. Intratracheal instillation of 200 microg ufCB in mice caused a significant and sustained increase of total proteins in bronchoalveolar lavage (BAL) fluid, with the maximal increase at 21 hr postinstillation. The influx of neutrophils did not significantly increase until 16 hr. It reached the highest level at 21 hr and returned to the basal level by 42 hr. Tumor necrosis factor-alpha was significantly elevated only at 4 hr. ufCB induced significant increases of VEGF in BAL fluid throughout the study period, with the peak increase at 16 hr. The nonsecreted isoform VEGF188 was not altered after 16 hr of exposure to ufCB. Moreover, there was a strong correlation between VEGF and total proteins in BAL fluid (R2 = 0.7352, p < 0.01). In vivo study supported the role of reactive oxygen species (ROSs) in ufCB-induced VEGF release and protein leakage. The involvement of ROSs was strengthened by the fact that interventions with N-acetylcysteine prevented ufCB-induced generation of ROSs and VEGF in vitro. Our study for the first time demonstrates that ufCB induces the production of VEGF, which is associated with the increase of alveolar-capillary permeability. The induction of VEGF by ufCB acts through an ROS-dependent pathway.

Activation and assembly of the NADPH oxidase: a structural perspective

The NADPH oxidase of professional phagocytes is a crucial component of the innate immune response due to its fundamental role in the production of reactive oxygen species that act as powerful microbicidal agents. The activity of this multi-protein enzyme is dependent on the regulated assembly of the six enzyme subunits at the membrane where oxygen is reduced to superoxide anions. In the resting state, four of the enzyme subunits are maintained in the cytosol, either through auto-inhibitory interactions or through complex formation with accessory proteins that are not part of the active enzyme complex. Multiple inputs are required to disrupt these inhibitory interactions and allow translocation to the membrane and association with the integral membrane components. Protein interaction modules are key regulators of NADPH oxidase assembly, and the protein-protein interactions mediated via these domains have been the target of numerous studies. Many models have been put forward to describe the intricate network of reversible protein interactions that regulate the activity of this enzyme, but an all-encompassing model has so far been elusive. An important step towards an understanding of the molecular basis of NADPH oxidase assembly and activity has been the recent solution of the three-dimensional structures of some of the oxidase components. We will discuss these structures in the present review and attempt to reconcile some of the conflicting models on the basis of the structural information available.

Induction of human spermine oxidase SMO(PAOh1) is regulated at the levels of new mRNA synthesis, mRNA stabilization and newly synthesized protein

The oxidation of polyamines induced by antitumour polyamine analogues has been associated with tumour response to specific agents. The human spermine oxidase, SMO(PAOh1), is one enzyme that may play a direct role in the cellular response to the antitumour polyamine analogues. In the present study, the induction of SMO(PAOh1) enzyme activity by CPENSpm [N1-ethyl-N11-(cyclopropyl)methyl-4,8,diazaundecane] is demonstrated to be a result of newly synthesized mRNA and protein. Inhibition of new RNA synthesis by actinomycin D inhibits both the appearance of SMO(PAOh1) mRNA and enzyme activity. Similarly, inhibition of newly synthesized protein with cycloheximide prevents analogue-induced enzyme activity. Half-life determinations indicate that stabilization of SMO(PAOh1) protein does not play a significant role in analogue-induced activity. However, half-life experiments using actinomycin D indicate that CPENSpm treatment not only increases mRNA expression, but also leads to a significant increase in mRNA half-life (17.1 and 8.8 h for CPENSpm-treated cells and control respectively). Using reporter constructs encompassing the SMO(PAOh1) promoter region, a 30-90% increase in transcription is observed after exposure to CPENSpm. The present results are consistent with the hypothesis that analogue-induced expression of SMO(PAOh1) is a result of increased transcription and stabilization of SMO(PAOh1) mRNA, leading to increased protein production and enzyme activity. These data indicate that the major level of control of SMO(PAOh1) expression in response to polyamine analogues exposure is at the level of mRNA.

Reactive oxygen species in ovarian physiology

Cells living under aerobic conditions always face oxygen paradox. Oxygen is necessary for cells to maintain their lives. However, reactive oxygen species such as superoxide radical ( ), hydroxyl radical (OH^-) and hydrogen peroxide (H₂O₂) are generated from oxygen and damage cells. Oxidative stress occurs as a consequence of excessive production of reactive oxygen species and impaired antioxidant defense systems. Antioxidant enzymes include: superoxide dismutase (SOD), which is a specific enzyme to scavenge superoxide radicals; copper-zinc SOD, located in the cytosol; and manganese SOD, located in the mitochondria. Both types of SOD belong to the first enzymatic step to scavenge superoxide radicals. It has been reported that a number of local factors such as cytokines, growth factors and eicosanoids are involved in the regulation of ovarian function, in addition to gonadotropins and ovarian steroid hormones. Since reactive oxygen species are generated and SOD is expressed in the ovary, there is a possibility that reactive oxygen species and SOD work as local regulators of ovarian function. The present review reports that reactive oxygen species and their scavenging systems play important roles in several processes of reproductive physiology, including follicular development, oocyte maturation, ovulation, corpus luteum function and follicular atresia. (Reprod Med Biol 2005; 4: 31- 45).

Proline suppresses apoptosis in the fungal pathogen Colletotrichum trifolii

The role of reactive oxygen species (ROS) in cell communication, control of gene expression, and oxygen sensing is well established. Inappropriate regulation of ROS levels can damage cells, resulting in a diseased state. In Colletotrichum trifolii, a fungal pathogen of alfalfa, the mutationally activated oncogenic fungal Ras (DARas) elevates levels of ROS, causing abnormal fungal growth and development and eventual apoptotic-like cell death but only when grown under nutrient-limiting conditions. Remarkably, restoration to the wild-type phenotype requires only proline. Here, we describe a generally unrecognized function of proline: its ability to function as a potent antioxidant and inhibitor of programmed cell death. Addition of proline to DARas mutant cells effectively quenched ROS levels and prevented cell death. Treating cells with inhibitors of ROS production yielded similar results. In addition, proline protected wild-type C. trifolii cells against various lethal stresses, including UV light, salt, heat, and hydrogen peroxide. These observations appear to be general because proline also protected yeast cells from lethal levels of the ROS-generating herbicide methyl viologen (paraquat), suggesting a common protective role for proline in response to oxidative stress. The ability of proline to scavenge intracellular ROS and inhibit ROS-mediated apoptosis may be an important and broad-based function of this amino acid in responding to cellular stress, in addition to its well established role as an osmolyte.

Apple polyphenol extracts prevent damage to human gastric epithelial cells in vitro and to rat gastric mucosa in vivo

BACKGROUND

Fresh fruit and vegetables exert multiple biological effects on the gastrointestinal mucosa.

AIM

To assess whether apple extracts counteract oxidative or indomethacin induced damage to gastric epithelial cells in vitro and to rat gastric mucosa in vivo.

METHODS

Apple extracts were obtained from freeze dried apple flesh of the "Annurca" variety. Cell damage was induced by incubating MKN 28 cells with xanthine-xanthine oxidase or indomethacin and quantitated by MTT. In vivo gastric damage was induced by indomethacin 35 mg/kg. Intracellular antioxidant activity was determined using the (2,2'-azinobis (3-ethylbenzothiazolin-6-sulfonate) method. Malondialdehyde intracellular concentration, an index of lipid peroxidation, was determined by high pressure liquid chromatography with fluorometric detection.

RESULTS

(1) Apple extracts decreased xanthine-xanthine oxidase or indomethacin induced injury to gastric epithelial cells by 50%; (2) catechin or chlorogenic acid (the main phenolic components of apple extracts) were equally effective as apple extracts in preventing oxidative injury to gastric cells; and (3) apple extracts (i) caused a fourfold increase in intracellular antioxidant activity, (ii) prevented its decrease induced by xanthine-xanthine oxidase, (iii) counteracted xanthine-xanthine oxidase induced lipid peroxidation, and (iv) decreased indomethacin injury to the rat gastric mucosa by 40%.

CONCLUSIONS

Apple extracts prevent exogenous damage to human gastric epithelial cells in vitro and to the rat gastric mucosa in vivo. This effect seems to be associated with the antioxidant activity of apple phenolic compounds. A diet rich in apple antioxidants might exert a beneficial effect in the prevention of gastric diseases related to generation of reactive oxygen species.

Cytidine 5'-diphosphocholine (CDP-choline) in stroke and other CNS disorders

Brain phosphatidylcholine (PC) levels are regulated by a balance between synthesis and hydrolysis. Pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1alpha/beta) activate phospholipase A(2) (PLA(2)) and PC-phospholipase C (PC-PLC) to hydrolyze PC. PC hydrolysis by PLA(2) releases free fatty acids including arachidonic acid, and lyso-PC, an inhibitor of CTP-phosphocholine cytidylyltransferase (CCT). Arachidonic acid metabolism by cyclooxygenases/lipoxygenases is a significant source of reactive oxygen species. CDP-choline might increase the PC levels by attenuating PLA(2) stimulation and loss of CCT activity. TNF-alpha also stimulates proteolysis of CCT. TNF-alpha and IL-1beta are induced in brain ischemia and may disrupt PC homeostasis by increasing its hydrolysis (increase PLA(2) and PC-PLC activities) and inhibiting its synthesis (decrease CCT activity). The beneficial effects of CDP-choline may result by counteracting TNF-alpha and/or IL-1 mediated events, integrating cytokine biology and lipid metabolism. Re-evaluation of CDP-choline phase III stroke clinical trial data is encouraging and future trails are warranted. CDP-choline is non-xenobiotic, safe, well tolerated, and can be considered as one of the agents in multi-drug treatment of stroke.

Cellular and molecular mechanisms in environmental and occupational inhalation toxicology

The central issue of this review are inflammatory changes that take place in the mucous membranes of the respiratory tract as a result of inhaled pollutants. Of particular relevance are dusts, SO(2), ozone, aldehydes und volatile organic compounds. Bioorganic pollutants, especially fragments of bacteria and fungi, occur predominantly in indoor dusts. They activate the toll-like/IL-1 receptor and lead to the activation of the transcription factor NF-κB for the release of numerous proinflammatory cytokines. Metals are predominant in ambient air dust particles. They induce the release of reactive oxygen species that cause damage to lipids, proteins and the DNA of the cell. As well as NF-κB, transcription factors that foster proliferation are activated via stress activated protein kinases. Organic compounds such as polycyclic aromatic hydrocarbons and nitroso-compounds of incomplete combustion processes activate additional via the cytosolic arylhydrocarbon receptor for detoxification enzymes. Sulphur dioxide leads to acid stress, and ozone to oxidative stress of the cell. This is accompanied by the release of proinflammatory cytokines via stress activated protein kinases. Aldehydes and volatile organic compounds activate the vanilloid receptor of trigeminal nerve fibres and induce a hyperreactivity of the mucous membrane via the release of nerve growth factors. The mechanisms described work synergistically and lead to a chronic inflammatory reaction of the mucous membranes of the upper respiratory tract that is regularly demonstrable in inhabitants of western industrial nations. It is unclear whether we are dealing here with a physiological inflammation or with an at least partially avoidable result of chronic pollutant exposure.

Role of reactive oxygen species in gynecologic diseases

Free radicals derived from molecular oxygen and nitrogen are highly reactive metabolites called reactive oxygen species (ROS). Cells continuously produce free radicals and ROS as part of the metabolic process. They are involved in the various functions of the reproductive system. Antioxidants are enzymes or compounds that scavenge and reduce the presence of free radicals. Normally, a balance exists between concentrations of reactive oxygen species and antioxidant scavenging systems. The disruption of the delicate balance between pro- and antioxidants results in oxidative stress. Oxidative stress has been implicated in embryo fragmentation, DNA damage, apoptosis and poor pregnancy outcome. It has also been implicated in a large number of gynecologic diseases, such as endometriosis, pre-eclampsia and maternal diabetes. The use of antioxidants may be beneficial in combating the harmful effects of oxidative stress in many of these diseases. The present review outlines the importance of these species in the pathology of various gynecologic diseases. (Reprod Med Biol 2004; 3: 177 - 199).

Vulnerability of central neurons to secondary insults after in vitro mechanical stretch

Mild traumatic brain injuries are of major public health significance. Neurons in such injuries often survive the primary mechanical deformation only to succumb to subsequent insults. To study mechanisms of vulnerability of injured neurons to secondary insults, we used an in vitro model of sublethal mechanical stretch. Stretch enhanced the vulnerability of the neurons to excitotoxic insults, causing nuclear irregularities, DNA fragmentation, and death suggestive of apoptosis. However, the DNA degradation was not attributable to classical (caspase mediated) or caspase-independent apoptosis. Rather, it was associated with profound stretch-induced mitochondrial dysfunction and the overproduction of reactive oxygen species (ROS). Sublethally stretched neurons produced surprisingly high levels of ROS, but these in isolation were insufficient to kill the cells. To be lethal, the ROS also needed to combine with nitric oxide (NO) to form the highly reactive species peroxynitrite. Peroxynitrite was not produced after stretch alone and arose only after combining stretch with an insult capable of stimulating NO production, such as NMDA or an NO donor. This explained the exquisite sensitivity of sublethally stretched neurons to a secondary NMDA insult. ROS scavengers and NO synthase (NOS) inhibitors prevented cell death and DNA degradation. Moreover, inhibiting neuronal NOS activation by NMDA using peptides that perturb NMDA receptor-postsynaptic density-95 interactions also reduced protein nitration and cell death, indicating that the reactive nitrogen species produced were neuronal in origin. Our data explain the mechanism of enhanced vulnerability of sublethally injured neurons to secondary excitotoxic insults and highlight the importance of secondary mechanisms to the ultimate outcome of neurons in mild neurotrauma.

Protective effect of heat shock protein 70 against oxidative stresses in human corneal fibroblasts

We evaluated DNA protection effect of heat shock protein (HSP) against cytotoxic effects of exogenous nitric oxide (NO) and reactive oxygen intermediate (ROI). Cultured human corneal fibroblasts were divided into 4 groups. Control (Group I) was not exposed to a sub-lethal heat treatment. Other 3 groups were exposed to 43 degrees C for 1 hr, then incubated at 37 degrees C during different duration (1, 6, 24 hr, Group II, III, IV, respectively). Expression pattern of HSP 70 was analyzed by Western blot. Cell viability was measured by MTT assay and the relationship between HSP 70 expression and DNA damage was examined by terminal deoxyribonucleotidyl transferase mediated dUTP-digoxigenin nick and labeling (TUNEL) stain and single cell gel electrophoresis. Expression pattern of HSP 70 was dependent on recovery times. Cell viability following heat treatment was significantly increased and the TUNEL positive cell number was decreased at 6 hr. In single cell gel electrophoresis, tail moments were increased in a dose-dependent manner by SNAP and X/XO. Following heat treatment, tail moments showed decreased significantly at 6 hr. These results suggest that induction of HSP 70 by sub-lethal heat treatment is closely related with cytoprotective effects against oxidative stresses in human corneal fibroblasts.

Melatonin and viral infections

The therapeutic effects of melatonin against viral infections, with emphasis on the Venezuelan equine encephalomyelitis (VEE), are reviewed. Melatonin has been shown to prevent paralysis and death in mice infected with the encephalomyocarditis virus and to decrease viremia. Melatonin also postpones the onset of the disease produced by Semliki Forest virus inoculation and reduces the mortality of West Nile virus-infected mice stressed by either isolation or dexamethasone injection. An increase in the host resistance to the virus via a peripheral immunostimulatory activity is considered responsible for these effects. It has also been demonstrated that melatonin protects some strains of mink against Aleutian disease, and prevents the reduction of B- and T-cells as well as Th1 cytokine secretion in mice infected with leukemia retrovirus. In VEE-infected mice, melatonin postpones the onset of the disease and death for several days and reduces the mortality rate. This protective effect seems to be due to the increase in the production of interleukin-1beta (IL-1beta), as 100% of the infected mice treated with melatonin die when IL-1beta is blocked with antimurine IL-1beta antibodies. Although melatonin administration raises serum levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), the mortality observed in neutralization experiments with the corresponding anticytokine antibodies, suggests that neither TNF-alpha nor IFN-gamma are essential for the protective effect of melatonin on murine VEE virus infection. Melatonin treatment also enhances the efficiency of immunization against the VEE virus. Reactive oxygen species have been implicated in the dissemination of this virus, and their deleterious effects may be diminished by melatonin. This indole inhibits nitric oxide synthetase activity and it is a potent scavenger of nitric oxide, which also plays an important role in the spread of the VEE virus. In conclusion, the immunomodulatory, antioxidant, and neuroprotective effects of melatonin suggest that this indole must be considered as an additional therapeutic alternative to fight viral diseases.

Methylglyoxal induces apoptosis mediated by reactive oxygen species in bovine retinal pericytes

One of the histopathologic hallmarks of early diabetic retinopathy is the loss of pericytes. Evidences suggest that the pericyte loss in vivo is mediated by apoptosis. However, the underlying cause of pericyte apoptosis is not fully understood. This study investigated the influence of methylglyoxal (MGO), a reactive alpha-dicarbonyl compound of glucose metabolism, on apoptotic cell death in bovine retinal pericytes. Analysis of internucleosomal DNA fragmentation by ELISA showed that MGO (200 to 800 microM) induced apoptosis in a concentration-dependent manner. Intracellular reactive oxygen species were generated earlier and the antioxidant, N-acetyl cysteine, inhibited the MGO-induced apoptosis. NF-kappaB activation and increased caspase-3 activity were detected. Apoptosis was also inhibited by the caspase-3 inhibitor, Z-DEVD-fmk, or the NF-kappaB inhibitor, pyrrolidine dithiocarbamate. These data suggest that elevated MGO levels observed in diabetes may cause apoptosis in bovine retinal pericytes through an oxidative stress mechanism and suggests that the nuclear activation of NF-kappaB are involved in the apoptotic process.

Applied and ecological aspects of oxidative-stress damage to bacterial spores and to oral microbes

Bacterial cells have adapted in a variety of ways to resist oxidative stresses and damage in their everyday lives in a predominantly aerobic world. The nearly universal occurrence of resistance mechanisms against oxidative stresses, particularly those due to reactive oxygen species (ROS), suggests that most, if not all, bacteria have to deal with oxidative assaults. A primary source of oxidative stress is aerobic metabolism, which leads to production of ROS such as hydrogen peroxide, superoxide radical, perhydroxyl radical, hydroxyl radical and a variety of other toxic metabolites, including organic peroxides and other organics or inorganics able to transfer electrons to sites of oxidative damage. Anaerobes as well as aerobic and facultative organisms are subject to oxidative stresses, often as a result of their own metabolism of O2 or that of associated facultative organisms. If anaerobes would just ignore oxygen instead of metabolizing it, they would not have to deal with toxic metabolites of their own making. Another major source of oxidative stress comes from the use of oxidative agents in the disinfection-sterilization industry. Notable examples are hypochlorite for water purification and hydrogen peroxide used for industrial sterilization. Antimicrobials such as isoniazide and mitomycin C also act oxidatively to cause damage. In this article, aseptic packaging and processing involving use of hydrogen peroxide for sterilization of packaging materials is reviewed as an example of oxidative stress imposed on bacterial spores and vegetative cells from outside the organisms or the microbial community. The other example considered is related to oral microbiology and infectious disease in which oxidative stress may arise from the metabolism of the oral microbiota or may come from outside through use of oral care products.

Biphasic response of ciprofloxacin in human fibroblast cell cultures

To investigate the possibility of the involvement of an oxidative stress induction in the mechanism of the cytotoxic effect of quinolone antibiotics, we examined the viability of human fibroblast cells exposed to ciprofloxacin (CPFX), and measured the levels of lipid peroxidation (LP), glutathione (GSH), and the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX). The data showed that the effect of CPFX on the viability of cells, as determined by neutral red uptake assay, was time-dependent, and the dose-response relation was biphasic. Cytotoxicity was not observed in the concentration range 5-150 mg/l CPFX when the cells were incubated for 24 h. In contrast, lower concentrations (5 and 12.5 mg/l) of CPFX increased the cell growth in all incubation periods tested. Marked decreases in the viability of fibroblasts were observed at concentrations 50 and 75 mg/l, and >/=50 mg/l, following 48 and 72 h exposure, respectively (p < 0.05). However, when the cells were exposed to > 75 mg/l CPFX for 48 h, no cytotoxicity was observed. By exposing fibroblast cultures to 75 mg/l CPFX for 48 h, an induction of LP enhancement and a marked decrease in intracellular GSH were observed. Vitamin E pretreatment of the cells lowered the level of LP, increased the total GSH content, and provided significant protection against CPFX-induced cytotoxicity. The biphasic effect of CPFX possibly resulted from the complex dose-dependent relationships between reactive oxygen species (ROS), cell proliferation, and cell viability. It was previously reported, in fact, for several cell models that ROS exert a biphasic effect on cell growth. Furthermore, cultured fibroblasts release their own free radicals, and the inhibition of endogenous ROS inhibits the fibroblast cell proliferation, whereas the effect of exogenous ROS is biphasic.

CD36 mediates the innate host response to beta-amyloid

Accumulation of inflammatory microglia in Alzheimer's senile plaques is a hallmark of the innate response to beta-amyloid fibrils and can initiate and propagate neurodegeneration characteristic of Alzheimer's disease (AD). The molecular mechanism whereby fibrillar beta-amyloid activates the inflammatory response has not been elucidated. CD36, a class B scavenger receptor, is expressed on microglia in normal and AD brains and binds to beta-amyloid fibrils in vitro. We report here that microglia and macrophages, isolated from CD36 null mice, had marked reductions in fibrillar beta-amyloid-induced secretion of cytokines, chemokines, and reactive oxygen species. Intraperitoneal and stereotaxic intracerebral injection of fibrillar beta-amyloid in CD36 null mice induced significantly less macrophage and microglial recruitment into the peritoneum and brain, respectively, than in wild-type mice. Our data reveal that CD36, a major pattern recognition receptor, mediates microglial and macrophage response to beta-amyloid, and imply that CD36 plays a key role in the proinflammatory events associated with AD.

The identification and characterization of oxidized RNAs in Alzheimer's disease

It has been shown that cytoplasmic RNA oxidation occurs to a great extent in the brains of Alzheimer's disease (AD) patients. The goal of this study was to isolate and identify oxidized RNA species in AD. We show that significant amounts of poly(A)+ mRNAs are oxidized in AD brains. RNA oxidation is not random but highly selective. Importantly, many identified oxidized mRNA species have been implicated in the pathogenesis of AD. Quantitative analysis revealed that some mRNA species are more susceptible to oxidative damage. We also investigated the biological consequence of oxidatively damaged mRNAs by expressing them in cell lines. Our data indicated that abnormal processing of proteins occurred to the oxidized mRNAs. This may implicate the potential contribution of RNA oxidation in the pathogenesis of AD.

Structural and biochemical studies of p21Ras S-nitrosylation and nitric oxide-mediated guanine nucleotide exchange

Ras is a guanine nucleotide-binding protein that cycles between inactive GDP-bound and active GTP-bound states to regulate a diverse array of cellular processes, including cell growth, apoptosis, and differentiation. The guanine nucleotide-bound state of Ras is tightly maintained by regulatory factors to promote regulated growth control. A class of regulatory molecules that lead to Ras activation are guanine nucleotide exchange factors (GEFs). Ras GEFs bind to Ras and facilitate GDP release, followed by GTP incorporation and Ras activation. Nitric oxide (NO) has also been shown to promote guanine nucleotide exchange (GNE) on Ras and increase cellular Ras-GTP levels, but the process by which NO-mediated GNE occurs is not clear. We initiated NMR structural and biochemical studies to elucidate how nitrosylation of Ras might lead to enhanced GNE. Surprisingly, our studies show that stable S-nitrosylation of Ras at Cys-118, does not affect the structure of Ras, its association with the Ras-binding domain of Raf (a downstream effector of Ras), or GNE rates relative to non-nitrosylated Ras. We have found, however, that the actual chemical process of nitrosylation, rather than the end-product of Ras S-nitrosylation, accounts for the enhanced GNE that we have observed and that has been previously observed by others.

Helicobacter pylori water soluble surface proteins prime human neutrophils for enhanced production of reactive oxygen species and stimulate chemokine production

BACKGROUNDS/AIMS

Chronic gastritis induced by Helicobacter pylori is characterised by considerable neutrophil infiltration into the gastric mucosa without mucosal invasion of bacteria. Bacteria have different characteristics with respect to their ability to stimulate human neutrophils to produce reactive oxygen species and chemokines. The aim of this study was to examine the effects of H pylori water extracts on the oxidative burst and chemokine production of human neutrophils.

METHODS

Helicobacter pylori cells were extracted by harvesting into distilled water and centrifugation. Neutrophils were incubated with H pylori water extracts and the production of reactive oxygen species was measured using luminol dependent chemiluminescence (LmCL). In addition, the concentrations of chemokines (interleukin 8 (IL-8), macrophage inflammatory protein 1-alpha (MIP1-alpha), and MIP1-beta) were measured by enzyme linked immunosorbent assay. Neutrophils were also stimulated by opsonised zymosan (OZ) after preincubation with H pylori water extracts.

RESULTS

Helicobacter pylori water extracts alone induced only a weak oxidative burst but preincubation of neutrophils with water extracts dose dependently enhanced the LmCL response stimulated by OZ. Helicobacter pylori water extracts also stimulated neutrophil IL-8 production, although MIP-1beta production was only stimulated weakly, and MIP-1alpha was not stimulated at all.

CONCLUSIONS

Helicobacter pylori products in water extracts may have a role in the activation and migration of neutrophils, which results in enhanced oxidative damage to gastric mucosa. These findings may explain the pathology of H pylori induced gastritis, in which there is little invasion of bacteria into the gastric mucosa.

Glutamate-dependent inhibition of dopamine release in striatum is mediated by a new diffusible messenger, H2O2

How glutamate regulates dopamine (DA) release in striatum has been a controversial issue. Here, we resolve this by showing that glutamate, acting at AMPA receptors, inhibits DA release by a nonclassic mechanism mediated by hydrogen peroxide (H(2)O(2)). Moreover, we show that GABA(A)-receptor activation opposes this process, thereby enhancing DA release. The influence of glutamate and GABA on DA release was assessed in striatal slices using carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Modulation by both transmitters was prevented by H(2)O(2)-metabolizing enzymes. In addition, the influence of GABA(A)-receptor activation was lost when AMPA receptors were blocked with GYKI-52466. Together, these data show that modulation of DA release by glutamate and GABA depends on H(2)O(2) generated downstream from AMPA receptors. This is the first evidence that endogenous glutamate can lead to the generation of reactive oxygen species under physiological conditions. We also show that inhibition of DA release by H(2)O(2) is mediated by sulfonylurea-sensitive K(+) channels: tolbutamide blocked DA modulation by glutamate and by GABA. The absence of ionotropic glutamate or GABA receptors on DA terminals indicates that modulatory H(2)O(2) is generated in non-DA cells. Thus, in addition to its known excitatory actions in striatum, glutamate mediates inhibition by generating H(2)O(2) that must diffuse from postsynaptic sites to inhibit presynaptic DA release via K(+)-channel opening. These findings have significant implications not only for normal striatal function but also for understanding disease states that involve DA and oxidative stress, including disorders as diverse as Parkinson's disease and schizophrenia.

The late increase in intracellular free radical oxygen species during apoptosis is associated with cytochrome c release, caspase activation, and mitochondrial dysfunction

Mitochondria play central roles in cellular metabolism and apoptosis and are a major source of reactive oxygen species (ROS). We investigated the role of ROS and mitochondria in radiation-induced apoptosis in multiple myeloma cells. Two distinct levels of ROS were generated following irradiation: a small increase observed early, and a pronounced late increase, associated with depletion of reduced glutathione (GSH) and collapse of mitochondrial membrane potential (deltapsi(m)). Exogenous ROS and caspase-3 induced deltapsi(m) drop and cytochrome c release from mitochondria, which could be prevented by molecular (dominant-negative caspase-9) and pharmacologic (zVAD-fmk) caspase inhibitors and overexpression of Bcl-2. Exogenous ROS also induced mitochondrial permeability transition (PT) pore opening and cytochrome c release in isolated mitochondria, which could be blocked by inhibition of PT with cyclosporin A. These results indicate that the late ROS production is associated with increased PT pore opening and decreased deltapsi(m), and GSH, events associated with caspase activation and cytochrome c release.

Mechanisms of hydrogen-peroxide-induced biphasic response in rat mesenteric artery

1. In phenylephrine (PHE) (1 micro M)-precontracted superior mesenteric arteries from adult rats, low concentration of hydrogen peroxide (H(2)O(2), 10-100 micro M) caused only contraction, while high concentration of H(2)O(2) (0.3-1 mM) caused a biphasic response: a transient contraction followed by a relaxation response. 2. Endothelium removal did not affect the biphasic response. 7,7-Dimethyl-(5Z,8Z)-eicosadienoic acid, diclofenac, furegrelate, or SQ 29548 greatly inhibited the contraction but did not affect the relaxation. 17-Octadecynoic acid, eicosatriynoic acid, ICI 198615, SQ 22536, or ODQ did not inhibit the biphasic response. 3. KCl at 40 mM inhibited the relaxation response to H(2)O(2) by 98+/-24%. 4-Aminopyridine (4-AP) inhibited while tetraethylammonium chloride (TEA), charybdotoxin, or glibenclamide attenuated the relaxation response. A combination of 4-AP, TEA and glibenclamide mimicked the effects of 40 mM KCl. Iberiotoxin, apamin, or barium chloride did not inhibit the relaxation response. 4. H(2)O(2) at 1 mM hyperpolarized membrane potential and reversibly augmented K(+) current in smooth muscle cells of mesenteric artery. These effects of H(2)O(2) were attenuated significantly by 4-AP. 5. In summary, in PHE-precontracted rat mesenteric artery: (1) the response to H(2)O(2) shifted qualitatively from contraction to a biphasic response as H(2)O(2) increased to 0.3 mM or higher; (2) the relaxation response is caused by the activation of K(+) channels, with voltage-dependent K(+) channels playing a primary role; and the contraction is likely to be mediated by thromboxane A(2); (3) the K(+) channel activation by H(2)O(2) is independent of phospholipase A(2), cyclooxygenase, lipoxygenase, cytochrome P450 monooxygenase, adenylate or guanylate cyclase.

Aluminium administration is associated with enhanced hepatic oxidant stress that may be offset by dietary vitamin E in the rat

It has been proposed that aluminium toxicity may be mediated, at least in part, by free radical generation. We have investigated the effects of aluminium lactate administration on indices of hepatic oxidant stress, and the consequences of concomitant dietary vitamin E, in male albino Wistar rats. Aluminium lactate was administered for 4 weeks, by ip injection at 10 mg aluminium/kg body weight. Groups of animals received a chow diet containing 0, 5, 15, or 20 mg vitamin E/g of food. A control group of rats received a normal chow diet, without being injected with aluminium. The rats were killed after 4 weeks, and blood and liver tissue removed for the measurement of aluminium and markers of oxidative stress. Plasma and liver aluminium levels were increased in all groups of animals receiving aluminium lactate (P < 0.01), although these levels were significantly reduced in rats receiving concomitant vitamin E (P < 0.05). Aluminium treatment was associated with significantly increased levels of hepatic reactive oxygen species (ROS) (P < 0.01) that were attenuated by concomitant vitamin E (P < 0.05). Hepatic catalase and reduced glutathione levels were both reduced in animals treated with aluminium (P < 0.05).

The anti-inflammatory actions of methotrexate are critically dependent upon the production of reactive oxygen species

1 The mechanism of action by which methotrexate (MTX) exerts its anti-inflammatory and immunosuppressive effects remains unclear. The aim of this study is to investigate the hypothesis that MTX exerts these effects via the production of reactive oxygen species (ROS). 2 Addition of MTX (100 nM-10 micro M) to U937 monocytes induced a time and dose dependent increase in cytosolic peroxide [peroxide](cyt) from 6-16 h. MTX also caused corresponding monocyte growth arrest, which was inhibited (P<0.05) by pre-treatment with N-acetylcysteine (NAC; 10 mM) or glutathione (GSH; 10 mM). In contrast, MTX induction of [peroxide](cyt) in Jurkat T cells was more rapid (4 h; P<0.05), but was associated with significant apoptosis at 16 h at all doses tested (P<0.05) and was significantly inhibited by NAC or GSH (P<0.05). 3 MTX treatment of monocytes (10 nM-10 micro M) for 16 h significantly reduced total GSH levels (P<0.05) independently of dose (P>0.05). However, in T-cells, GSH levels were significantly elevated following 30 nM MTX treatment (P<0.05) but reduced by doses exceeding 1 micro M compared to controls (P<0.05). 4 MTX treatment significantly reduced monocyte adhesion to 5 h and 24 h LPS (1 micro g ml(-1)) activated human umbilical vein endothelial cells (HUVEC; P<0.05) but not to resting HUVEC. Pre-treatment with GSH prevented MTX-induced reduction in adhesion. 5 In conclusion, ROS generation by MTX is important for cytostasis in monocytes and cytotoxicity T-cells. Furthermore, MTX caused a reduction in monocyte adhesion to endothelial cells, where the mechanism of MTX action requires the production of ROS. Therefore its clinical efficacy can be attributed to multiple targets.

Alcohol, oxidative stress, and free radical damage

Reactive oxygen species (ROS) are small, highly reactive, oxygen-containing molecules that are naturally generated in small amounts during the body's metabolic reactions and can react with and damage complex cellular molecules such as fats, proteins, or DNA. Alcohol promotes the generation of ROS and/or interferes with the body's normal defense mechanisms against these compounds through numerous processes, particularly in the liver. For example, alcohol breakdown in the liver results in the formation of molecules whose further metabolism in the cell leads to ROS production. Alcohol also stimulates the activity of enzymes called cytochrome P450s, which contribute to ROS production. Further, alcohol can alter the levels of certain metals in the body, thereby facilitating ROS production. Finally, alcohol reduces the levels of agents that can eliminate ROS (i.e., antioxidants). The resulting state of the cell, known as oxidative stress, can lead to cell injury. ROS production and oxidative stress in liver cells play a central role in the development of alcoholic liver disease.

Overexpression of CYP2D6 attenuates the toxicity of MPP+ in actively dividing and differentiated PC12 cells

Clonal pheochromocytoma cell lines overexpressing cytochrome P450 2D6 (CYP2D6) were established. CYP2D6 was localized in the endoplasmic reticulum, and its enzymatic activity in the microsomal fraction was confirmed by using high performance liquid chromatography analysis with [guanidine-14C]debrisoquine as a substrate. Overexpression of CYP2D6 protected both actively dividing and differentiated cells against the toxic effects of 1-methyl-4-phenylpyridinium ion at the concentration range of 20-40 microM, as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The production of reactive oxygen species in the mitochondria was suppressed. The cytotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was unchanged in both actively dividing and differentiated cells overexpressing CYP2D6 versus mock-transfected controls at concentrations up to 500 microM. These results suggest that the lowered enzyme activity of CYP2D6 in individuals termed "poor metabolizers" may represent a risk factor from exposure to select neurotoxicants.

Glucose deprivation induces mitochondrial dysfunction and oxidative stress in PC12 cell line

Glucose metabolism plays a pivotal role in many physiological and pathological conditions. To investigate the effect of hypoglycemia (obtained by glucose deprivation) on PC12 cell line, we analyzed the cell viability, mitochondrial function (assessed by MTT reduction, cellular ATP level, mitochondrial transmembrane potential), and the level of reactive oxygen species (ROS) after glucose deprivation (GD). Upon exposure to GD, ROS level increased and MTT reduction decreased immediately, intracellular ATP level increased in the first 3 hours, followed by progressive decrease till the end of GD treatment, and the mitochondrial transmembrane potential (deltapsi(m)) dropped after 6 hours. Both necrosis and apoptosis occurred apparently after 24 hours which was determined by nuclei staining with propidium iodide(PI) and Hoechst 33342. These data suggested that cytotoxicity of GD is mainly due to ROS accumulation and ATP depletion in PC12 cells.

Impact of oxygen stress and energy availability on membrane stability of plant cells

This article reviews the relationship between the energy status of plant cells under O(2) stress (e.g. waterlogging) and the maintenance of membrane intactness, using information largely derived from suspension cultures of anoxia-intolerant potato cells. Energy-related parameters measured were fermentation end-products (ethanol, lactate, alanine), respiratory rate, ATP, adenylate energy charge, nitrate reductase activity and biomass. ATP synthesis rates were calculated from the first four parameters. Reactive oxygen species were estimated from H(2)O(2) and superoxide levels, and the enzymatic detoxification potential from the activity levels of catalase and superoxide dismutase. Structure-related parameters were total fatty acids, free fatty acids (FFAs), lipid hydroperoxides, total phospholipids, N-acylphosphatidylethanolamine (NAPE) and cell viability. The following issues are addressed in this review: (1) what is the impact of anoxia on membrane lipids and how does this relate to energy status; (2) does O(2) per se play a role in these changes; (3) under which conditions and to what extent does lipid peroxidation occur upon re-aeration; and (4) can the effects of re-aeration be distinguished from those of anoxia? The emerging picture is a reappraisal of the relative contributions of anoxia and re-aeration. Two successive phases (pre-lytic and lytic) characterize potato cells under anoxia. They are connected by a threshold in ATP production rate, below which membrane lipids are hydrolysed to FFAs, and NAPE increases. Since lipid peroxidation occurs only when cells are reoxygenated during the lytic phase, its biological relevance in an already damaged system is questionable.

Reactive oxygen species, antioxidant mechanisms and serum cytokine levels in cancer patients: impact of an antioxidant treatment

OBJECTIVE

So far, it is not well established whether oxidative stress found in cancer patients results from an increased production of oxidants in the body or from a failure of physiological antioxidant systems. To further investigate this question we have assessed the blood levels of reactive oxygen species as a marker of free radicals producing oxidative stress and the most relevant of the physiological body enzymes counteracting reactive oxygen species, namely glutathione peroxidase and superoxide dismutase. Serum levels of proinflammatory cytokines and IL-2 were also investigated. All these parameters were studied in relation to the clinically most important index of disease progression, namely Performance Status (ECOG PS). We also tested the reducing ability of different antioxidant agents on reactive oxygen species levels by measuring the increase in glutathione peroxidase activity, and the reduction of serum levels of IL-6 and TNF.

DESIGN, SETTING AND SUBJECTS

We carried out an open non randomized study on 28 advanced stage cancer patients (stage III, 10.7%, and stage IV, 89.3%) with tumours at different (8) sites: all were hospitalized in the Medical Oncology Dept, University of Cagliari Interventions. The patients were divided into 5 groups and a different antioxidant treatment was administered to each group. The selected antioxidants were: alpha lipoic acid 200 mg/day orally, N-acetylcysteine 1800 mg/day i.v. or carboxycysteine-lysine salt 2.7 g/day orally, amifostine 375 mg/day i.v., reduced glutathione 600 mg/day i.v., vitamin A 30000 IU/day orally plus vitamin E 70 mg/day orally plus Vitamin C 500 mg/day orally. The antioxidant treatment was administered for 10 consecutive days.

RESULTS

Our results show that all but one of the antioxidants tested were effective in reducing reactive oxygen species levels and 2 of them (cysteine-containing compounds and amifostine) had the additional effect of increasing glutathione peroxidase activity. Comprehensively, the "antioxidant treatment" was found to have an effect both on reactive oxygen species levels and glutathione peroxidase activity. The antioxidant treatment also reduced serum levels of IL-6 and TNF. Patients in both ECOG PS 0-1 and ECOG PS 2-3 responded to antioxidant treatment.

Copper/zinc superoxide dismutase attenuates neuronal cell death by preventing extracellular signal-regulated kinase activation after transient focal cerebral ischemia in mice

Recent studies have revealed that activation of extracellular signal-regulated kinase (ERK) may contribute to apoptosis, a cell death process involved in oxidative stress. We examined phosphorylation of ERK1/2 and oxidative stress after transient focal cerebral ischemia (FCI) using transgenic (Tg) mice that overexpress copper/zinc superoxide dismutase (SOD1). The mice were subjected to 60 min of middle cerebral artery (MCA) occlusion by intraluminal suture blockade followed by 1, 4, and 24 hr of reperfusion. Immunohistochemistry and Western blot analysis showed that phospho-ERK1 was markedly increased in the cortex within the MCA territory at 1 hr of reperfusion (p < 0.01), followed by a decrease at 24 hr in wild-type mice. Double staining with phospho-ERK1/2 and neuron-specific nuclear protein showed that phospho-ERK1/2 was primarily expressed in neurons. In SOD1 Tg mice, phospho-ERK1/2 was prominently reduced compared with nonischemic controls, shown by immunohistochemistry. Western blot analysis confirmed a significant decrease in phospho-ERK1/2 1 hr after FCI in the ischemic cortex (p < 0.005). Apoptotic-related DNA fragmentation was reduced in the ischemic cortex of SOD1 Tg mice compared with wild-type mice using a cell death assay. These results suggest that phosphorylation of ERK1/2 may be involved in apoptosis or cell death after transient FCI and that SOD1 may attenuate apoptotic cell death mediated by the mitogen-activated protein kinase/ERK pathway.

NADPH oxidase(s): new source(s) of reactive oxygen species in the vascular system?

Reactive oxygen species play an important role in a variety of (patho)physiological vascular processes. Recent publications have produced evidence of a role for putative non-phagocyte NADP oxidase(s) in the vascular production of reactive oxygen species. In the present review, we discuss the detection of the different components of NADP oxidase(s) in the vascular system, together with the putative role of reactive oxygen species produced by vascular NADPH oxidase(s), in both in vitro and in vivo studies.

Induction of apoptosis in hepatocellular carcinoma cell lines by emodin

Previous experiments have shown that emodin is highly active in suppressing the proliferation of several tumor cell lines. However, it is not clear that emodin can induce growth inhibition of hepatoma cells. We have found that emodin induces apoptotic responses in the human hepatocellular carcinoma cell lines (HCC) Mahlavu, PLC/PRF/5 and HepG2. The addition of emodin to these three cell lines led to inhibition of growth in a time- and dose-dependent manner. Emodin generated reactive oxygen species (ROS) in these cells which brought about a reduction of the intracellular mitochondrial transmembrane potential (DeltaPsim), followed by the activation of caspase-9 and caspase-3, leading to DNA fragmentation and apoptosis. Our findings demonstrate that ROS and the resulting oxidative stress play a pivotal role in apoptosis. Preincubation of hepatoma cell lines with the hydrogen peroxide-scavenging enzyme, catalase (CAT) and cyclosporin A (CsA), partially inhibited apoptosis. These results demonstrate that enhancement of generation of ROS, DeltaPsim disruption and caspase activation may be involved in the apoptotic pathway induced by emodin.

Ebselen attenuates oxidative stress-induced apoptosis via the inhibition of the c-Jun N-terminal kinase and activator protein-1 signalling pathway in PC12 cells

1: Ebselen (2-phenyl-1,2-benzisoselenazol-3[2H]-one) is a selenoorganic compound exhibiting both glutathione peroxidase activity and antioxidant activity. Although it has been reported that ebselen is effective for oxidative stress-induced neuronal damage both in vivo and clinically, the precise mechanisms of the efficacy have not yet been elucidated. Thus, we hypothesized that ebselen may affect reactive oxygen species-induced mitogen-activated protein (MAP) kinase activation in cultured PC12 cells. 2: Our findings showed that hydrogen peroxide (H(2)O(2)) stimulated rapid and significant activation of extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38 in PC12 cells, which is a model of catecholamine-containing neurons. 3: H(2)O(2)-induced JNK activation was inhibited by ebselen, whereas ERK1/2 and p38 activation by H(2)O(2) were not affected by ebselen. 4: Inhibition by ebselen of H(2)O(2)-induced hydroxyl radical generation in PC12 cells was observed using electron paramagnetic resonance measurements. Ebselen also inhibited H(2)O(2)-induced increases in DNA binding activity of activator protein-1 (AP-1), a downstream transcription factor of JNK, composed of the c-Jun homo/heterodimer. 5: Finally, pretreatment of cells with ebselen resulted in a significant recovery from cell death including apoptosis by H(2)O(2) in PC12 cells. 6 These findings suggest that ebselen attenuates oxidative stress-induced neuronal cell death through the inhibition of the JNK and AP-1 signalling pathway. Thus, inhibition of JNK by ebselen may imply its usefulness for treatment of ischaemic cerebral diseases relevant to neuronal cell death.

Implication of mitochondria-derived ROS and cardiolipin peroxidation in N-(4-hydroxyphenyl)retinamide-induced apoptosis

We have studied the effect of N-(4-hydroxyphenyl)retinamide on either malignant human leukaemia cells or normal cells and investigated its mechanism of action. We demonstrate that 4HPR induces reactive oxygen species increase on mitochondria at a target between mitochondrial respiratory chain complex I and II. Such oxidative stress causes cardiolipin peroxidation which in turn allows cytochrome c release to cytosol, caspase-3 activation and therefore apoptotic consumption. Moreover, this apoptotic pathway seems to be bcl-2/bax independent and count only on malignant cells but not normal nor activated lymphocytes.

The molecular mechanism in activation-induced cell death of an Ag-reactive B cell clone

TPA-1 is a subclone of B cell hybridomas established by somatic hybridization using B cells of A/J mice immunized with TNP-LPS, and expresses a receptor for TNP on the cell membrane. The present study showed that TPA-1 was induced to apoptotic cell death upon treatment with TNP-BSA. Therefore, TPA-1 is considered to provide a good model for the study on activation-induced cell death of mature B cells induced by soluble antigen. TNP-BSA treatment caused the generation of a large amount of intracellular reactive oxygen species (ROS) of TPA-1, and the addition of the monovalent thiol-reactive compound: monochlorobimane (MCB) rescued it from apoptosis as well as the antioxidant reagent: N-acetyl-L-cysteine. Furthermore, MCB markedly inhibited the generation of ROS and prevented the disruption of mitochondrial membrane potential that was induced by TNP-BSA treatment. In addition, it counteracted the effect of TNP-BSA on the expression of the Bcl-2 family, resulting in down-regulation of Bax and Bad and up-regulation of Bcl-XL. Taken together, these results suggest strongly that oxidative stress of mitochondria may be involved directly in apoptotic cell death by engagement of antigen receptors on mature B cells with soluble antigen.

Superoxide dismutase activities of spermatozoa and seminal plasma are not correlated with male infertility

Abnormal reactive oxygen species (ROS) production is associated with defective sperm function. Superoxide dismutase (SOD) is related with the scavenging of seminal ROS. We aimed to determine the effect of SOD activities of spermatozoa and seminal plasma on sperm quality. Semen samples from infertile couples who consented to the analyses were divided into two groups: 1) normospermia (n = 20); and 2) oligoasthenozoospermia (n = 31). The SOD activities of the spermatozoa and seminal plasma were measured by determining the inhibition of pyrogallol autoxidation. The SOD activities of spermatozoa and seminal plasma in both groups were compared. The relationships between the SOD activities and the sperm qualities were determined. We noted that SOD activities of sperm/seminal plasma in both groups were nonsignificantly different (group 1 vs. 2 = 0.77 +/- 0.33/0.84 +/- 0.40 U/mg protein for sperm, and 0.66 +/- and 0.36/0.83 +/- 0.47 U/ml for seminal plasma). SOD activities of sperm/seminal plasma were positively but nonsignificantly correlated with the sperm motility (SOD of sperm = 0.0008 x motility + 0.67; SOD of seminal plasma = 0.0006 x motility + 0.81) and concentration (SOD of sperm = 0.0006 x concentration + 0.67; SOD of seminal plasma = 0.0021 x concentration + 0.73). We concluded that SOD activities of sperm and seminal plasma were nonsignificantly correlated with the seminal quality. It appears that the SOD survey is not a useful tool for determining sperm fertilization potential.

Selective blockade of mGlu5 metabotropic glutamate receptors is protective against methamphetamine neurotoxicity

Methamphetamine (MA), a widely used drug of abuse, produces oxidative damage of nigrostriatal dopaminergic terminals. We examined the effect of subtype-selective ligands of metabotropic glutamate (mGlu) receptors on MA neurotoxicity in mice. MA (5 mg/kg, i.p.; injected three times, every 2 hr) induced, 5 d later, a substantial degeneration of striatal dopaminergic terminals associated with reactive gliosis. MA toxicity was primarily attenuated by the coinjection of the noncompetitive mGlu5 receptor antagonists 2-methyl-6-(phenylethynyl)pyridine and (E)-2-methyl-6-styrylpyridine both at 10 mg/kg, i.p.). In contrast, the mGlu1 receptor antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (10 mg/kg, i.p.), and the mGlu2/3 receptor agonist (-)-2-oxa-4-aminocyclo[3.1.0]hexane-4,6-dicarboxylic acid (1 mg/kg, i.p.), failed to affect MA toxicity. mGlu5 receptor antagonists reduced the production of reactive oxygen species but did not reduce the acute stimulation of dopamine release induced by MA both in striatal synaptosomes and in the striatum of freely moving mice. We conclude that endogenous activation of mGlu5 receptors enables the development of MA neurotoxicity and that mGlu5 receptor antagonists are neuroprotective without interfering with the primary mechanism of action of MA.

Diabetes, oxidative stress and physical exercise

Oxidative stress, an imbalance between the generation of reactive oxygen species and antioxidant defense capacity of the body, is closely associated with aging and a number of diseases including cancer, cardiovascular diseases, diabetes and diabetic complications. Several mechanisms may cause oxidative insult in diabetes, although their exact contributions are not entirely clear. Accumulating evidence points to many interrelated mechanisms that increase production of reactive oxygen and nitrogen species or decrease antioxidant protection in diabetic patients. In modern medicine, regular physical exercise is an important tool in the prevention and treatment of diseases including diabetes. Although acute exhaustive exercise increases oxidative stress, exercise training has been shown to up regulate antioxidant protection. This review aims to summarize the mechanisms of increased oxidative stress in diabetes and with respect to acute and chronic exercise.

Potentiation of hippocampal synaptic transmission by superoxide requires the oxidative activation of protein kinase C

Recent evidence suggests that reactive oxygen species (ROS), including superoxide, are not only neurotoxic but function as small messenger molecules in normal neuronal processes such as synaptic plasticity. Consistent with this idea, we show that brief incubation of hippocampal slices with the superoxide-generating system xanthine/xanthine oxidase (X/XO) produces a long-lasting potentiation of synaptic transmission in area CA1. We found that X/XO-induced potentiation was associated with a persistent superoxide-dependent increase in autonomous PKC activity that could be isolated via DEAE column chromatography. The X/XO-induced potentiation was blocked by the inhibition of PKC, indicating that the superoxide-dependent increase in autonomous PKC activity was necessary for the potentiation. We also found that X/XO-induced potentiation and long-term potentiation (LTP) occluded one another, suggesting that these forms of plasticity share similar cellular mechanisms. In further support of this idea, we found that a persistent, superoxide-dependent increase in autonomous PKC activity isolated via DEAE column chromatography also was associated with LTP. Taken together, our findings indicate that X/XO-induced potentiation and LTP share similar cellular mechanisms, including superoxide-dependent increases in autonomous PKC activity. Finally, our findings suggest that superoxide, in addition to its well known role as a neurotoxin, also can be considered a small messenger molecule critical for normal neuronal signaling.

Inducing the cell cycle arrest and apoptosis of oral KB carcinoma cells by hydroxychavicol: roles of glutathione and reactive oxygen species

Hydroxychavicol (HC; 10 - 50 microM), a betel leaf component, was found to suppress the 2% H(2)O(2)-induced lucigenin chemiluminescence for 53 - 75%. HC (0.02 - 2 microM) was also able to trap superoxide radicals generated by a xanthine/xanthine oxidase system with 38 - 94% of inhibition. Hydroxyl radicals-induced PUC18 plasmid DNA breaks was prevented by HC (1.6 - 16 microM). A 24-h exposure of KB cells to HC (0.5, 1 mM) resulted in 54 - 74% cell death as analysed by a 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. HC (10, 50 microM) further suppressed the growth of KB cells (15 and 76%, respectively). Long-term colony formation of KB cells was inhibited by 51% with 10 microM HC. Pretreatment of KB cells with 100 microM HC inhibited the attachment of KB cells to type I collagen and fibronectin by 59 and 29%, respectively. Exposure of KB cells to 0.1 mM HC for 24 h resulted in cell cycle arrest at late S and G2/M phase. Increasing the HC concentration to 0.25 and 0.5 mM led to apoptosis as revealed by detection of sub-G(0)/G(1) peaks with a concomitant decrease in the number of cells residing in late S and G(2)/M phase. Inducing the apoptosis of KB cells by HC was accompanied by marked depletion in reduced form of GSH (>0.2 mM) and the increasing of reactive oxygen species production (>0.1 mM) as analysed by CMF- and DCF-single cell fluorescence flow cytometry. These results indicate that HC exerts antioxidant property at low concentration. HC also inhibits the growth, adhesion and cell cycle progression of KB cells, whereas its induction of KB cell apoptosis (HC>0.1 mM) was accompanied by cellular redox changes.

Cyclosporin A-induced free radical generation is not mediated by cytochrome P-450

1. Reactive oxygen species (ROS) have been proposed to play a role in the side effects of the immunosuppressive drug cyclosporin A (CsA). 2. The aim of this study was to investigate whether cytochrome P-450 (CYP) dependent metabolism of CsA could be responsible for ROS generation since it has been suggested that CsA may influence the CYP system to produce ROS. 3. We show that CsA (1 -- 10 microM) generated antioxidant-inhibitable ROS in rat aortic smooth muscle cells (RASMC) using the fluorescent probe 2,7-dichlorofluorescin diacetate. 4. Using cytochrome c as substrate, we show that CsA (10 microM) did not inhibit NADPH cytochrome P-450 reductase in microsomes prepared from rat liver, kidney or RASMC. 5. CsA (10 microM) did not uncouple the electron flow from NADPH via NADPH cytochrome P-450 reductase to the CYP enzymes because CsA did not inhibit the metabolism of substrates selective for several CYP enzymes that do not metabolize CsA in rat liver microsomes. 6. CsA (10 microM) did not generate more radicals in CYP 3A4 expressing immortalized human liver epithelial cells (T5-3A4 cells) than in control cells that do not express CYP 3A4. 7. Neither diphenylene iodonium nor the CYP 3A inhibitor ketoconazole were able to block ROS formation in rat aortic smooth muscle or T5-3A4 cells. 8. These results demonstrate that CYP enzymes do not contribute to CsA-induced ROS formation and that CsA neither inhibits NADPH cytochrome P-450 reductase nor the electron transfer to the CYP enzymes.