Reactive oxygen species as cellular messengers

Redox control of calcium channels: from mechanisms to therapeutic opportunities

Calcium plays an integral role in cellular function. It is a well-recognized second messenger necessary for signaling cellular responses, but in excessive amounts can be deleterious to function, causing cell death. The main route by which calcium enters the cytoplasm is either from the extracellular compartment or internal addistores via calcium channels. There is good evidence that calcium channels can respond to pharmacological compounds that reduce or oxidize thiol groups on the channel protein. In addition, reactive oxygen species such as hydrogen peroxide and superoxide that can mediate oxidative pathology also mediate changes in channel function via alterations of thiol groups. This review looks at the structure and function of calcium channels, the evidence that changes in cellular redox state mediate changes in channel function, and the role of redox modification of channels in disease processes. Understanding how redox modification of the channel protein alters channel structure and function is providing leads for the design of therapeutic interventions that target oxidative stress responses.

Liver-homing of purified glucose oxidase: a novel in vivo model of physiological hepatic oxidative stress (H2O2)

BACKGROUND/AIMS

Reactive oxygen species (ROS), such as H2O2, are implicated in normal and pathological liver function. However, due to the lack of suitable in vivo models of ROS generation the (patho) physiological relevance of H2O2 remains controversial.

METHODS

We established a novel model of sustained hepatic H2O2 release using intravenous administration of purified Aspergillus niger glucose oxidase (GOX) in rats.

RESULTS

GOX is rapidly cleared from the blood stream and almost exclusively localizes to Kupffer cells. GOX maintained its ability to generate H2O2 over 24h. While sublethal GOX doses induced hepatocellular necrosis, our morphological and functional studies show that lower levels of GOX which generate H2O2 comparable to release by inflammatory cells are non-toxic and do not induce histological inflammation. However, these non-toxic H2O2 levels increased oxidized glutathione and induced heme oxygenase 1 in the liver. In addition, several hepatocyte transporters were downregulated, while no decrease of bile formation, a sensitive marker of liver function, was observed.

CONCLUSIONS

Our in vivo model allows to study the effects of extracellular H2O2 in the liver as is released by inflammatory cells. Thus analysis of the role of this major ROS in the absence of confounding inflammatory cofactors will be possible.

Curcumin-induced GADD153 upregulation: Modulation by glutathione

As we reported previously, GADD153 is upregulated in colon cancer cells exposed to curcumin. In the present study, we ascertained the involvement of glutathione and certain sulfhydryl enzymes associated with signal transduction in mediating the effect of curcumin on GADD153. Curcumin-induced GADD153 gene upregulation was attenuated by reduced glutathione (GSH) or N-acetylcysteine (NAC) and potentiated by the glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine (BSO). Additionally, GSH and NAC decreased the intracellular content of curcumin. Conversely, curcumin decreased intracellular glutathione and also increased the formation of reactive oxygen species (ROS) in cells, but either GSH or NAC prevented both of these effects of curcumin. In affecting the thiol redox status, curcumin caused activation of certain sulfhydryl enzymes involved in signal transduction linked to GADD153 expression. Curcumin increased the expression of the phosphorylated forms of PTK, PDK1, and PKC-delta, which was attenuated by either GSH or NAC and potentiated by BSO. Furthermore, selective inhibitors of PI3K and PKC-delta attenuated curcumin-induced GADD153 upregulation. Collectively, these findings suggest that a regulatory thiol redox-sensitive signaling cascade exists in the molecular pathway leading to induction of GADD153 expression as caused by curcumin.

Reciprocal effects of glucose on the process of cell death induced by calcium ionophore or H2O2 in rat lymphocytes

We have examined the effects of glucose at high concentrations on the process of cell death induced by excessive increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) or oxidative stress in rat lymphocytes. The cell death elicited by the excessive increase in [Ca(2+)](i) seemed to be induced by an activation of Ca(2+)-dependent K(+) channels because the inhibitors for Ca(2+)-dependent K(+) channels attenuated the decrease in cell viability. Glucose at 30-50mM augmented the decrease in cell viability by the excessive increase in [Ca(2+)](i). It was not specific for glucose because it was the case for sucrose or NaCl, suggesting an involvement of increased osmolarity in adverse action of glucose. On the contrary, glucose protected the cells suffering from oxidative stress induced by H(2)O(2), one of reactive oxygen species. It was also the case for fructose or sucrose, but not for NaCl. The process of cell death induced by H(2)O(2) started, being independent from the presence of glucose. Glucose delayed the process of cell death induced by H(2)O(2). Sucrose and fructose also protected the cells against oxidative stress. The reactivity of sucrose to reactive oxygen species is lower than those of glucose and fructose. The order in the reactivity cannot explain the protective action of glucose. Glucose at high concentrations exerts reciprocal actions on the process of cell death induced by the oxidative stress and excessive increase in [Ca(2+)](i).

Electron-transfer capacity of catechin derivatives and influence on the cell cycle and apoptosis in HT29 cells

Galloylated and nongalloylated catechin conjugates with cysteine derivatives have been synthesized and evaluated for their capacity to scavenge free radicals and to influence crucial functions (cell cycle, apoptosis) in HT29 colon carcinoma cells. We show that the nonphenolic part of the molecule modified the capacity of catechins to donate hydrogen atoms and to transfer electrons to free radicals. Nongalloylated derivatives did not significantly influence either the cell cycle or apoptosis. Among the galloylated species, 4beta-[S-(O-ethyl-cysteinyl)]epicatechin 3-O-gallate, which showed a high electron-transfer capacity (5 e- per molecule), arrested the cell cycle and induced apoptosis as expected for galloylated catechins such as tea (-)-epigallocatechin 3-O-gallate. 4beta-[S-(N-Acetyl-O-methyl-cysteinyl)]epicatechin 3-O-gallate, which showed the highest hydrogen-donating capacity (10 H per molecule) while keeping the electron-transfer capacity low (2.9 e- per molecule), did not trigger any significant apoptosis. The gallate moiety did not appear to be sufficient for the pro-apoptotic effect of the catechin derivatives in HT29 cells. Instead, a high electron-transfer capacity is more likely to be behind this effect. The use of stable radicals sensitive exclusively to electron transfer may help to design molecules with either preventive scavenging action (high hydrogen donation, low electron transfer) or therapeutic pro-apoptotic activity (high electron transfer).

Acid stress adaptation protects Saccharomyces cerevisiae from acetic acid-induced programmed cell death

In this work evidence is presented that acid stress adaptation protects Saccharomyces cerevisiae from acetic acid-mediated programmed cell death. Exponential-phase yeast cells, non-adapted or adapted to acid stress by 30 min incubation in rich medium set at pH 3.0 with HCl, have been exposed to increasing concentrations of acetic acid and time course changes of cell viability have been assessed. Adapted cells, in contrast to non-adapted cells, when exposed to 80 mM acetic acid for 200 min did not display loss of cell viability associated to morphological alterations typical of apoptosis. Thus, 80 mM acetic acid death-inducing conditions were selected to further characterize the early molecular events leading to such active cell death process. Catalase was specifically activated during acid stress adaptation and protection against acetic acid-induced death was associated with maintenance of its activity during treatment with 80 mM acetic acid. On the other hand, intracellular superoxide dismutase activity was found present at comparable levels both in adapted and in dying yeast cells, excepting in non-adapted cells which displayed a maximum activity value after 15 min acetic acid exposure, corresponding to more than 80% cell viability. This study gives first experimental evidence that H2O2, rather than superoxide, detoxification may have a major role in preventing yeast cell death in response to acetic acid. The results, as a whole, suggest that commitment of S. cerevisiae to a programmed cell death process in response to acetic acid is mediated through a ROS-dependent apoptotic pathway.

Survival pathways triggered by peroxynitrite in cells belonging to the monocyte/macrophage lineage

Peroxynitrite, a highly reactive nitrogen species, promotes in U937 cells (a promonocytic cell line) a mitochondrial permeability transition (MPT)-dependent necrosis. An initial event triggered by peroxynitrite (i.e., inhibition of complex III of the mitochondrial respiratory chain) is responsible for the time-dependent formation of H(2)O(2), essential for the occurrence of cell death. Otherwise non-toxic concentrations of peroxynitrite nevertheless commit cells to MPT-dependent necrosis, which is however prevented by a cytoprotective signaling driven by arachidonic acid (AA) released by the cytosolic PLA(2) isoform. Interestingly, the mechanism whereby delayed formation of H(2)O(2) promotes toxicity in cells exposed to intrinsically toxic concentrations of peroxynitrite is independent of the accumulation of additional damage. Cell death is in fact mediated by inhibition of the AA-dependent cytoprotective signaling. Exogenous AA, however, prevented toxicity also under these conditions. An additional point to be made is that the major findings obtained using U937 cells were reproduced in different cell types belonging to the monocyte/macrophage lineage. Hence, within the context of the inflammatory response, monocytes and macrophages may cope with peroxynitrite by using AA, a signaling molecule largely available at the inflammatory sites.

Near-real-time determination of hydrogen peroxide generated from cigarette smoke

The ability to monitor hydrogen peroxide (H2O2) in aqueous smoke extracts will advance our understanding of the relationship between cigarette smoke-induced oxidative stress, inflammation, and disease and help elucidate the pathways by which the various smoke constituents exert their pathogenic effects. We have demonstrated, for the first time, the measurement of H2O2 production from cigarette smoke without prior separation of the sample. Cigarettes were tested on a commercial smoking machine, such that the whole smoke or gas vapor phase was bubbled through phosphate buffered saline solution at pH 7.4. Aliquots of these solutions were analyzed using an Amplex Red/horseradish peroxidase fluorimetric assay that required only a 2 minute incubation time, facilitating the rapid, facile collection of data. Catalase was used to demonstrate the selectivity and specificity of the assay for H2O2 in the complex smoke matrix. We measured approximately 7-8 microM H2O2 from two reference cigarettes (i.e., 1R4F and 2R4F). We also observed 9x more H2O2 from whole smoke bubbled samples compared to the gas vapor phase, indicating that the major constituent(s) responsible for H2O2 formation reside in the particulate phase of cigarette smoke. Aqueous solutions of hydroquinone and catechol, both of which are particulate phase constituents of cigarette smoke, generated no H2O2 even though they are free radical precursors involved in the production of reactive oxygen species in the smoke matrix.

Acute hypoxia differentially regulates K+ channels. Implications with respect to cardiac arrhythmia

The first ion channels demonstrated to be sensitive to changes in oxygen tension were K(+) channels in glomus cells of the carotid body. Since then a number of hypoxia-sensitive ion channels have been identified. However, not all K(+) channels respond to hypoxia alike. This has raised some debate about how cells detect changes in oxygen tension. Because ion channels respond rapidly to hypoxia it has been proposed that the channel is itself an oxygen sensor. However, channel function can also be modified by thiol reducing and oxidizing agents, implicating reactive oxygen species as signals in hypoxic events. Cardiac ion channels can also be modified by hypoxia and redox agents. The rapid and slow components of the delayed rectifier K(+) channel are differentially regulated by hypoxia and beta-adrenergic receptor stimulation. Mutations in the genes that encode the subunits for the channel are associated with Long QT syndrome and sudden cardiac death. The implications with respect to effects of hypoxia on the channel and triggering of cardiac arrhythmia will be discussed.

Blue light differentially alters cellular redox properties

Blue light (lambda = 380-500 nm) historically has been used to initiate polymerization of biomaterials and recently has been proposed as a therapeutic agent. New evidence suggests that cell-type-specific responses result from redox changes induced by exposure to blue light. Cultured cells were exposed to defined doses of blue light, equivalent to exposure times of 10 s and 2 min, to achieve energies of 5 J/cm2 and 60 J/cm2, respectively, after which (a) viable cell number, (b) cellular protein profiles, (c) mitochondrial succinate dehydrogenase (SDH) activity, (d) total reactive oxygen species (ROS), and (e) induction of apoptosis were compared to that of nonexposed control cultures. Results showed that blue-light exposure arrested monocyte cell growth and increased levels of peroxiredoxins. SDH activity of normal epidermal keratinocytes (NHEK) was slightly enhanced by blue light, whereas identical treatment of OSC2 oral tumor cells resulted in significant suppression of SDH activity. Blue-light exposure generally induced higher levels of total ROS in OSC2 cells than in NHEK. Finally, only OSC2 cells exhibited signs of apoptosis via Annexin V staining following exposure to blue light. These data support the central hypothesis that blue light induces an oxidative stress response in cultured cells resulting in cell-type-specific survival outcomes. The identification of oxidative stress as a mediator of the effects of blue light is a critical first step in defining its biological risks and therapeutic opportunities.

Activation of ERK or inhibition of JNK ameliorates H(2)O(2) cytotoxicity in mouse renal proximal tubule cells

BACKGROUND

Our previous studies suggest that the balance between the activation of extracellular signal-regulated kinase (ERK) and the c-Jun N-terminal/stress-activated protein kinase (JNK) might determine cell fate following oxidant injury in vivo.

METHODS

The mouse proximal tubule cell line (TKPTS) was used to study hydrogen peroxide (H(2)O(2))-induced death and survival. The role of ERK and JNK in this process was studied by using adenoviruses that contain either a constitutively active mitogen-activated protein kinase kinase 1 (MEK1) or a dominant-negative JNK. Acridine orange plus ethidium bromide staining was applied to distinguish between viable, apoptotic, and necrotic cells following H(2)O(2) treatment. We analyzed cell cycle events by fluorescence-activated cell sorter (FACS) analysis and the phosphorylation status of ERK and JNK by Western blotting.

RESULTS

TKPTS cells survived a moderate level of oxidative stress (0.5 mM/L H(2)O(2)) via temporary growth arrest, while high dose of H(2)O(2) (1 mM/L) caused extensive necrosis. Survival was associated with activation of both ERK and JNK, while death was associated with JNK activation only. Prior adenovirus-mediated up-regulation of ERK or inhibition of JNK function increased the survival (8- or 7-fold, respectively) of TKPTS cells after 1 mmol/L H(2)O(2) treatment. Interestingly, ERK activation and, thus, survival was associated with growth arrest not proliferation.

CONCLUSION

We demonstrate that oxidant injury-induced necrosis could be ameliorated by either up-regulation of endogenous ERK or by inhibition of JNK-related pathways. These results directly demonstrate that the intracellular balance between prosurvival and prodeath mitogen-activated protein kinases (MAPKs) determine proximal tubule cell survival from oxidant injury and reveal possible mediators of survival.

Genome-wide analysis of redox-regulated genes in a dinoflagellate

In this study, the effects of 1 mM sodium nitrite, a reactive nitrogen species (RNS) generator, and 0.5 mM paraquat, which produces reactive oxygen species (ROS), on gene expression in the marine dinoflagellate species Pyrocystis lunula were investigated using microarrays containing 3500 complementary DNAs (cDNAs). A total of 246 differentially expressed genes were identified under these treatments: 204 genes were specifically regulated in response to nitrite and 37 genes specifically to paraquat. Only six genes showed a dependence on both nitrite and paraquat, indicating that the two agents act predominantly via distinct pathways. Although many of these redox-regulated genes encode proteins from a diverse range of functional categories, the majority of them (68%) represent novel sequences. Temporary abnormal spherical cells occurred in nitrite-treated cultures, but not in those exposed to paraquat, suggesting that this response involves a specific pathway triggered by RNS. The genes involved include one that encodes a transcription factor unique to dinoflagellates (HPl), and genes encoding proteins similar to those regulating developmental processes in plants and animals such as NYD-SP5, shaggy and calcium-dependent kinases, the COP9 signalosome complex, ubiquitin-related proteases and a metacaspase.

Effect of the oxidative phosphorylation uncoupler 2,4-dinitrophenol on hypoxia-inducible factor-regulated gene expression in bovine blastocysts

In cattle embryos, development to the blastocyst stage is improved in the presence of 10 μm 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, coincident with an increase in glycolytic activity following embryonic genome activation. The present study examined redox-sensitive gene expression and embryo development in response to the addition of DNP post-compaction. 2,4-Dinitrophenol increased the expression of hypoxia-inducible factor 1α and 2α (HIF1α, HIF2α) mRNA. Although HIF1α protein remained undetectable in bovine blastocysts, HIF2α protein was localised within the nucleus of trophectoderm and inner cell mass (ICM) cells of blastocysts cultured in the presence or absence of DNP, with a slight increase in staining evident within the ICM in blastocysts cultured in the presence of DNP. However, the expression of GLUT1 and VEGF mRNA, genes known to be regulated by HIFs, was unaffected by the addition of DNP to the culture. Although the development of Grade 1 and 2 blastocysts was unaltered by the addition of DNP post compaction in the present study, a significant increase in the proportion of ICM cells was observed. Results indicate that 10 μm DNP improves the quality of bovine embryos, coincident with increased HIF2α protein localisation within ICM cells and increased HIFα mRNA levels. Therefore, the results demonstrate redox-regulated expression of HIF2.

Differential regulation of the slow and rapid components of guinea-pig cardiac delayed rectifier K+ channels by hypoxia

The aim of this study was to examine the effects of acute hypoxia on the slow (I(Ks)) and rapid (I(Kr)) components of the native delayed rectifier K+ channel in the absence and presence of the beta-adrenergic receptor agonist isoproterenol (isoprenaline; Iso) using the whole-cell configuration of the patch-clamp technique. Hypoxia reversibly inhibited basal I(Ks). The effect could be mimicked by exposing the cells to the thiol-specific reducing agent dithiothreitol (DTT) and attenuated upon exposure of cells to the membrane-impermeant thiol-specific oxidizing compound 5,5'-dithio-bis[2-nitrobenzoic acid] (DTNB). In the presence of hypoxia, the K(0.5) for activation of I(Ks) by Iso was significantly decreased from 18.3 to 1.9 nm. DTT mimicked the effect of hypoxia on the sensitivity of I(Ks) to Iso while DTNB had no effect. Hypoxia increased the sensitivity of I(Ks) to histamine and forskolin suggesting that the effect of hypoxia is not occurring at the beta-adrenergic receptor. The increase in sensitivity of I(Ks) to Iso could be attenuated with addition of PKCbeta peptide to the pipette solution. While hypoxia and DTT inhibited basal I(Ks) they were without effect on I(Kr.) In addition, Iso did not appear to alter the magnitude of I(Kr) in the absence or presence of hypoxia. These data suggest that hypoxia regulates native I(Ks) through two distinct mechanisms: direct inhibition of basal I(Ks) and an increase in sensitivity to Iso that occurs downstream from the beta-adrenergic receptor. Both mechanisms appear to involve redox modification of thiol groups. In contrast native I(Kr) does not appear to be regulated by Iso, hypoxia or redox state.

Mitochondrial localization of reactive oxygen species by dihydrofluorescein probes

Mitochondria are the main source of reactive oxygen species (ROS). The aim of this work was to verify the ROS generation in situ in HeLa cells exposed to prooxidants and antioxidants (menadione, tert-butyl hydroperoxide, antimycin A, vitamin E, N-acetyl-L-cysteine, and butylated hydroxytoluene) using the ROS-sensitive probes 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate di-acetomethyl ester (DCDHF) and dihydrofluorescein diacetate (DHF). Mitochondria were counterstained with the potential-sensitive probe tetramethylrhodamine methyl ester perchlorate (TMRM). Both DCDHF and DHF were able to detect the presence of ROS in mitochondria, though with distinct morphological features. DCDHF fluorescence was invariably blurred, smudged, and spread over the cytoplasm surrounding the major mitochondrial clusters. On the contrary, DHF fluorescence was sharp and delineated thin filaments which corresponded in all details to TMRM-stained mitochondria. These data suggest that DCDHF does not reach the mitochondrial matrix but is oxidized by ROS released by mitochondria in the cytosol. On the other hand, DHF enters mitochondria and reacts with ROS released in the matrix. Cytosolic (DCDHF+) ROS but not matrix (DHF+) ROS, were significantly decreased by vitamin E. N-acetyl-L-cysteine was effective in reducing DCDHF and DHF photooxidation in the medium, but was unable to reduce intracellular ROS. ROS generation was accompanied by partial mitochondrial depolarization.

New approach to the simultaneous analysis of catecholamines and tyrosines in biological fluids

New high-performance liquid chromatographic (HPLC) methods with amperometric-CoulArray detection were developed for simultaneous analyses of norepinephrine, epinephrine, L-DOPA, dopamine, 3-nitrotyrosine, m-, o-, and p-tyrosines. Overall, detection limit was in the low pmol range with amperometry, and in the low fmol range for the CoulArray method. Linear (r2 = 0.99) detector performances were observed in the ranges of 2-200 pmol with amperometry, and 0.2-20 pmol for the CoulArray method. Analytical precision values were better than 80 and 95% for HPLC-amperometry and HPLC-CoulArray method, respectively. These methods offer sensitivity, specificity, minimal sample requirement, and especially the HPLC-CoulArray method allows simultaneous assessment of various similar biomolecules.

Redox-sensitive mechanisms of phytochemical-mediated inhibition of cancer cell proliferation (review)

Phytochemicals are potential cancer chemopreventive agents, based partly on cellular research establishing that phytochemicals inhibit the proliferation of cancer cells. To elucidate the mechanism of phytochemicals, a basic understanding is needed of what stimulates cancer cell proliferation. Cancer cells, particularly those that are highly invasive or metastatic, may require a certain level of oxidative stress to maintain a balance between undergoing either proliferation or apoptosis. They constitutively generate large but tolerable amounts of H2O2 that apparently function as signaling molecules in the mitogen-activated protein kinase pathway to constantly activate redox-sensitive transcription factors and responsive genes that are involved in the survival of cancer cells as well as their proliferation. With such a reliance of cancer cells on H2O2 it follows that if the excess H2O2 can be scavenged by phenolic phytochemicals having antioxidant activity, the oxidative stress-responsive genes can be suppressed and consequently cancer cell proliferation inhibited. On the other hand, phenolic phytochemicals and another group of phytochemicals known as isothiocyanates can induce the formation of H2O2 to achieve an intolerable level of high oxidative stress in cancer cells. As an early response, the stress genes are activated. However, when the critical threshold for cancer cells to cope with the induced oxidative stress has been reached, key cellular components such as DNA are damaged irreparably. In conjunction, genes involved in initiating cell cycle arrest and/or apoptosis are activated. Therefore, phytochemicals can either scavenge the constitutive H2O2 or paradoxically generate additional amounts of H2O2 to inhibit the proliferation of cancer cells.

Redox control of iron regulatory proteins

Iron regulatory proteins, IRP1 and IRP2, are cytoplasmic proteins of the iron-sulfur cluster isomerase family and serve as major post-transcriptional regulators of cellular iron metabolism. They bind to 'iron responsive elements' (IREs) of several mRNAs and thereby control their translation or stability. IRP1 and IRP2 respond to alterations in intracellular iron levels, but also to other signals such as nitric oxide (NO) and reactive oxygen species (ROS). The redox regulation of IRP1 and IRP2 provides direct links between the control of iron homeostasis and oxidative stress.

Decreasing cellular hydrogen peroxide with catalase mimics the effects of hypoxia on the sensitivity of the L-type Ca2+ channel to beta-adrenergic receptor stimulation in cardiac myocytes

In cardiac myocytes, hypoxia inhibits the basal L-type Ca2+ current (I(Ca-L)) and increases the sensitivity of I(Ca-L) to beta-adrenergic receptor stimulation. We investigated whether hydrogen peroxide (H2O2) is involved in the hypoxic response. Guinea pig ventricular myocytes were dialyzed with catalase, which specifically catalyzes the conversion of H2O2 to H2O and oxygen, and then I(Ca-L) was recorded during exposure to isoproterenol (Iso). Catalase decreased the K(0.5) for activation of I(Ca-L) by Iso from 2.7+/-0.3 nmol/L (in cells dialyzed with heat-inactivated catalase) to 0.4+/-0.1 nmol/L. The increase in sensitivity to Iso by catalase may be attenuated when cells are preexposed to H2O2. A significant increase in sensitivity of I(Ca-L) to Iso was recorded when mitochondrial function was inhibited with myxothiazol or FCCP, suggesting that the source of H2O2 was from the mitochondria. Prior exposure of cells to H2O2 attenuated the inhibition of basal I(Ca-L) during hypoxia and the increase in sensitivity of I(Ca-L) to Iso during hypoxia. Additionally, extracellularly applied catalase mimicked the effect of hypoxia on basal I(Ca-L). Measurement of the rate of production of hydrogen peroxide using 5- (and 6-)chloromethyl-2', 7'-dichlorodihydrofluorescein diacetate acetyl ester indicated that hypoxia was associated with a significant decrease in the production of hydrogen peroxide in the cells. These data suggest that hypoxia mediates changes in channel activity through a lowering in H2O2 levels and that H2O2 is a key intermediate in modifying basal channel activity and the beta-adrenergic responsiveness of the channel during hypoxia.

Inactivation of the 2-oxo acid dehydrogenase complexes upon generation of intrinsic radical species

Self-regulation of the 2-oxo acid dehydrogenase complexes during catalysis was studied. Radical species as side products of catalysis were detected by spin trapping, lucigenin fluorescence and ferricytochrome c reduction. Studies of the complexes after converting the bound lipoate or FAD cofactors to nonfunctional derivatives indicated that radicals are generated via FAD. In the presence of oxygen, the 2-oxo acid, CoA-dependent production of the superoxide anion radical was detected. In the absence of oxygen, a protein-bound radical concluded to be the thiyl radical of the complex-bound dihydrolipoate was trapped by alpha-phenyl-N-tert-butylnitrone. Another, carbon-centered, radical was trapped in anaerobic reaction of the complex with 2-oxoglutarate and CoA by 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Generation of radical species was accompanied by the enzyme inactivation. A superoxide scavenger, superoxide dismutase, did not protect the enzyme. However, a thiyl radical scavenger, thioredoxin, prevented the inactivation. It was concluded that the thiyl radical of the complex-bound dihydrolipoate induces the inactivation by 1e- oxidation of the 2-oxo acid dehydrogenase catalytic intermediate. A product of this oxidation, the DMPO-trapped radical fragment of the 2-oxo acid substrate, inactivates the first component of the complex. The inactivation prevents transformation of the 2-oxo acids in the absence of terminal substrate, NAD+. The self-regulation is modulated by thioredoxin which alleviates the adverse effect of the dihydrolipoate intermediate, thus stimulating production of reactive oxygen species by the complexes. The data point to a dual pro-oxidant action of the complex-bound dihydrolipoate, propagated through the first and third component enzymes and controlled by thioredoxin and the (NAD+ + NADH) pool.

Sensitive and real-time determination of H2O2 release from intact peroxisomes

Peroxisomes are essential and ubiquitous cell organelles having a key role in mammalian lipid and oxygen metabolism. The presence of flavine oxidases makes them an important intracellular source of H(2)O(2): an obligate product of peroxisomal redox reactions and a key reactive oxygen species. Peroxisomes proliferate in response to external signals triggered by peroxisome-proliferator-activated receptor signalling pathways. Peroxisome-derived oxidative stress as a consequence of this proliferation is increasingly recognized to participate in pathologies ranging from carcinogenesis in rodents to alcoholic and non-alcoholic steatosis hepatitis in humans. To date, no sensitive approach exists to record H(2)O(2) turnover of peroxisomes in real time. Here, we introduce a sensitive chemiluminescence method that allows the monitoring of H(2)O(2) generation and degradation in real time in suspensions of intact peroxisomes. Importantly, removal, as well as release of, H(2)O(2) can be assessed at nanomolar, non-toxic concentrations in the same sample. Owing to the kinetic properties of catalase and oxidases, H(2)O(2) forms fast steady-state concentrations in the presence of various peroxisomal substrates. Substrate screening suggests that urate, glycolate and activated fatty acids are the most important sources for H(2)O(2) in rodents. Kinetic studies imply further that peroxisomes contribute significantly to the beta-oxidation of medium-chain fatty acids, in addition to their essential role in the breakdown of long and very long ones. These observations establish a direct quantitative release of H(2)O(2) from intact peroxisomes. The experimental approach offers new possibilities for functionally studying H(2)O(2) metabolism, substrate transport and turnover in peroxisomes of eukaryotic cells.

The role of oxidative stress in mechanisms of metal-induced carcinogenesis

Metals are necessary for the normal functioning of cells and the survival of organisms. However, exposure to higher than the physiological levels of several metals may lead to tumor development. Although the exact molecular mechanism(s) of metal-induced carcinogenesis is not clear, a vast body of evidence indicates that metal-induced generation of reactive oxygen species (ROS) may play a central role in this process. Two main pathways of ROS-induced effects are discussed in this chapter: (i) increased DNA damage induced either directly or indirectly by impeding DNA repair, and (ii) modulation of nuclear transcriptional factor activities, such as NF-kappaB and AP-1, through mitogen-activated protein kinases signal transduction mechanisms.

Aberrant redox regulation in human metastatic melanoma cells compared to normal melanocytes

Melanocytes and melanoma cells contain melanin, a complex polymer that modulates redox changes in these cells. Relative intracellular hydrogen peroxide levels measured by dichlorodihydrofluorescein are similar in the two cell types, but the levels of superoxide anion measured by dihydroethidium were markedly increased in melanoma cells. Chelator-induced oxidative stress is efficiently suppressed by melanocytes without substantial recruitment of the transcription factors NF-kappaB and AP-1 as measured by electrophoretic mobility shift assay and quantitated by densitometry or by a change in frequency of apoptosis as determined by annexin V binding. In contrast, NF-kappaB in melanoma cells is strongly recruited by changes in redox status and exhibits a correlative relationship to intracellular hydrogen peroxide (but not superoxide anion). However, the response of the NF-kappaB pathway to intracellular hydrogen peroxide is anomalous, including downregulation of p65 and IkappaBalpha RNA expression (Northern blot). Additionally, recruitment of AP-1 binding in melanoma cells was directly correlated with intracellular levels of superoxide anion (but not hydrogen peroxide). Neither the degree of NF-kappaB nor AP-1 binding in melanoma cells was related to the frequency of apoptosis. The responsiveness of NF-kappaB and AP-1 recruitment to intracellular levels of hydrogen peroxide and superoxide anion without concomitant control of apoptosis provides a general mechanism by which these cells can escape noxious injury (e.g., chemotherapy). The marked enhancement of apoptosis in melanoma cells by chelators indicates, however, that this alteration can be circumvented and offers a unique therapeutic window to explore.

Novel effects of nitric oxide

Nitric oxide (NO), a simple free radical gas, elicits a surprisingly wide range of physiological and pathophysiological effects. NO interacts with soluble guanylate cyclase to evoke many of these effects. However, NO can also interact with molecular oxygen and superoxide radicals to produce reactive nitrogen species that can modify a number of macromolecules including proteins, lipids, and nucleic acids. NO can also interact directly with transition metals. Here, we have reviewed the non--3',5'-cyclic-guanosine-monophosphate-mediated effects of NO including modifications of proteins, lipids, and nucleic acids.

Different regulatory mechanisms modulate the expression of a dinoflagellate iron-superoxide dismutase

Regulation of antioxidant enzymes is critical to control the levels of reactive oxygen species in cell compartments highly susceptible to oxidative stress. In this work, we studied the regulation of a chloroplastic iron superoxide dismutase (Fe-SOD) from Lingulodinium polyedrum (formerly Gonyaulax polyedra) under different physiological conditions. A cDNA-encoding Fe-SOD was isolated from this dinoflagellate, showing high sequence similarity to cyanobacterial, algal, and plant Fe-SODs. Under standard growth conditions, on a 12:12-h light-dark cycle, Lingulodinium polyedrum Fe-SOD exhibited a daily rhythm of activity and cellular abundance with the maximum occurring during the middle of the light phase. Northern analyses showed that this rhythmicity is not related to changes in Fe-SOD mRNA levels, indicative of translational regulation. By contrast, conditions of metal-induced oxidative stress resulted in higher levels of Fe-SOD transcripts, suggesting that transcriptional control is responsible for increased protein and activity levels. Daily (circadian) and metal-induced up-regulation of Fe-SOD expression in L. polyedrum are thus mediated by different regulatory pathways, allowing biochemically distinct changes appropriate to oxidative challenges.

Hydroxyl radical adduct of 5-aminosalicylic acid: A potential marker of ozone-induced oxidative stress

The use of 5-aminosalicylic acid in assessment of reactive oxygen species formation was investigated by in vitro Fenton and ozonation reactions, and by in vivo ozone-exposure experiments. Enzymatic hydroxylation was evaluated by a microsomal assay. Fischer 344 male rats (250 g) injected with 5-aminosalicylic acid (100 mg·kg-1 i.p.; 30 min) were exposed to ozone (0, 1, 2 ppm; nose only, 2 h); bronchoalveolar lavage, lung homogenates, and plasma were recovered. Oxidation products of 5-aminosalicylic acid were as follows: salicylic acid, by deamination; 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid, from radical or enzymatic hydroxylation; 5-amino-2-hydroxy-N,N'-bis(3-carboxy-4-hydroxyphenyl)-1,4-benzoquinonediimine, a condensation product of oxidized 5-aminosalicylic acid; and 5-amino-2,3,4,6-tetrahydroxybenzoic acid, attributed to hydroxyl radical attack without deamination, identified by HPLC electrochemical (HPLC-EC) detector system analysis and by GC-MS analysis of trimethylsilyl derivatives. 5-Aminotetrahydroxybenzoic acid was not formed enzymatically. 5-Aminotetrahydroxybenzoic acid, but not 5-aminosalicylic acid, was significantly elevated in bronchoalveolar lavage (+86%) and lung homogenates (+56%) in response to 2 ppm ozone (p < 0.05); no significant changes were detected in plasma. The data indicate that hydroxylation of 5-aminosalicylic acid is a potential specific probe for in vivo oxidative stress.Key words: 5-aminosalicylic acid, biomarker, free radical scavenging, hydroxyl radical, ozone.

Reactive oxygen species (ROS)-induced ROS release: a new phenomenon accompanying induction of the mitochondrial permeability transition in cardiac myocytes

We sought to understand the relationship between reactive oxygen species (ROS) and the mitochondrial permeability transition (MPT) in cardiac myocytes based on the observation of increased ROS production at sites of spontaneously deenergized mitochondria. We devised a new model enabling incremental ROS accumulation in individual mitochondria in isolated cardiac myocytes via photoactivation of tetramethylrhodamine derivatives, which also served to report the mitochondrial transmembrane potential, DeltaPsi. This ROS accumulation reproducibly triggered abrupt (and sometimes reversible) mitochondrial depolarization. This phenomenon was ascribed to MPT induction because (a) bongkrekic acid prevented it and (b) mitochondria became permeable for calcein ( approximately 620 daltons) concurrently with depolarization. These photodynamically produced "triggering" ROS caused the MPT induction, as the ROS scavenger Trolox prevented it. The time required for triggering ROS to induce the MPT was dependent on intrinsic cellular ROS-scavenging redox mechanisms, particularly glutathione. MPT induction caused by triggering ROS coincided with a burst of mitochondrial ROS generation, as measured by dichlorofluorescein fluorescence, which we have termed mitochondrial "ROS-induced ROS release" (RIRR). This MPT induction/RIRR phenomenon in cardiac myocytes often occurred synchronously and reversibly among long chains of adjacent mitochondria demonstrating apparent cooperativity. The observed link between MPT and RIRR could be a fundamental phenomenon in mitochondrial and cell biology.

Sensitive and nonenzymatic measurement of hydrogen peroxide in biological systems

The increasing demand in detecting H(2)O(2) under various experimental conditions is only partly fulfilled by most conventional peroxidase-based assays. This article describes a sensitive and nonenzymatic H(2)O(2) assay that is based on the chemiluminescence reaction of luminol with hypochlorite. It allows the determination of H(2)O(2) down to nanomolar concentrations. Actual H(2)O(2) concentrations rather than a turnover of H(2)O(2) can be determined in monolayer cultures, perfusates, suspensions of intact cells, organelles, and crude homogenates. One of the strengths of this assay is that it may be used to assess fast enzyme kinetics (catalase, glutathione peroxidase, oxidases) at very low H(2)O(2) concentrations. Its use together with a glucose oxidase/catalase system appears to be a powerful tool in studying signal functions of H(2)O(2) in various biological systems on a quantitative basis. Several applications are discussed in detail to demonstrate the technical requirements and analytical potentials.

Oestrogen metabolism in lymphangioleiomyomatosis: catechol-O-methyltransferase pathway is not involved

BACKGROUND

Lymphangioleiomyomatosis (LAM) is an uncommon lung disease for which no effective method of treatment has been found. The predilection of LAM for premenopausal women has led to the assumption that hormonal factors play an important role in the pathogenesis of this disease. The aim of this study was to determine if women with LAM manifest alterations in the catechol-O-methyltransferase (COMT) pathway which is essential for preventing the generation of oestrogen derived reactive oxygen species (ROS).

METHODS

Blood samples were collected from 15 women with LAM and compared with appropriate controls. The distribution of high and low activity alleles of COMT was determined with a PCR based RFLP assay. The enzymatic activity of COMT was measured in each sample and the potential presence of a circulating inhibitor of COMT was determined. Since an alteration in the COMT pathway could increase the oxidative stress, the plasma concentration of malondialdehyde (MDA), a secondary product generated from lipid peroxidation, has been used as an internal marker.

RESULTS

The distribution of high and low activity alleles of COMT (named COMT(HH), COMT(LL), and COMT(HL)) was similar in the two groups with proportions of 40%, 7%, and 53%, respectively, in the women with LAM and 38%, 6%, and 56% in the control subjects. The mean (SD) COMT activity was 24.2 (12.3) pmol/min/mg protein in women with LAM and 24.1 (6.3) pmol/min/mg protein in the control group. Incubation of plasma from women in the two groups with a preparation of commercial COMT showed that no detectable COMT inhibitor was present. The plasma concentration of MDA in the women with LAM was also not significantly different from control subjects.

CONCLUSIONS

This study shows that there are no significant alterations in the COMT pathway of women with LAM. It is therefore unlikely that alterations in oestrogen mediated cell signalling pathways are mediated by oxidants derived from an excess of catecholoestrogens in LAM.

Oxidative stress and neural dysfunction in Down syndrome

Total or partial trisomy of chromosome 21 occurs with relatively high frequency and is responsible for the occurrence of Down syndrome. Phenotypically, individuals with Down syndrome display characteristic morphological features and a variety of clinical disorders. One of the challenges for researchers in this field has been to ascertain and understand the relationship between the Down syndrome phenotype with the gene dosage effect resulting from trisomy of chromosome 21. Much attention therefore, has been given towards investigating the consequences of overexpressing chromosome 21-linked genes. In particular, an extensive analysis of SOD1 and APP have provided important insights as to how perturbations in the expression of their respective genes may contribute to the Down syndrome phenotype. In this review we will highlight studies which support a key role for SOD1 and APP in the pathogenesis of neural abnormalities observed in individuals with Down syndrome. Central to this relationship is how the redox state of the cell is affected and its consequences to neural function and integrity.

Lysozyme photo-oxidation by singlet oxygen: properties of the partially inactivated enzyme

This work studies the behaviour of partially inactivated lysozyme formed by the effect of singlet oxygen, which was obtained through the irradiation of the native enzyme solution with polychromatic visible light using Methylene Blue as a sensitizer. The polyacrylamide gel analysis of the partially inactivated lysozyme solution shows the presence of different protein fractions. One of them, which corresponds to 53% of the original enzyme, has the same migration as the native enzyme. The others are a mixture of fractions (47%) that show slower migration to the cathode. When this experiment is carried out in the presence of sodium dodecyl sulfate, only one fraction is obtained, which rules out the presence of covalently aggregated forms of lysozyme. The partially inactivated lysozyme has lost 74% of the fluorescence emission of the tryptophan (Trp) residues. By using the anionic quencher iodide, it is determined that 45 and 36% of the fluorescence emission arising from the native and partially inactivated enzyme, respectively, are due to Trp residues exposed to the solvent. Michaelis-Menten constants (K(in)) of 0.296 and 0.511 (mg/ml) and maximum initial rates (Vmax) of 0.295 and 0.190 (mg/ml min) are determined for the native and the partially inactivated enzyme solutions, respectively. The same inactivation profile is found when the denaturing effect of increasing urea concentration on both the native and partially inactivated lysozyme is studied. It is postulated that the partially inactivated lysozyme solution is composed of one protein fraction with enzymatic activity similar to that of the native enzyme and also of a mixture of fractions (47% of the total enzyme) with very low activity and characterized by a high tryptophan photo-oxidation.

Reduction of nitrite to nitric oxide catalyzed by xanthine oxidoreductase

Xanthine oxidase (XO) was shown to catalyze the reduction of nitrite to nitric oxide (NO), under anaerobic conditions, in the presence of either NADH or xanthine as reducing substrate. NO production was directly demonstrated by ozone chemiluminescence and showed stoichiometry of approximately 2:1 versus NADH depletion. With xanthine as reducing substrate, the kinetics of NO production were complicated by enzyme inactivation, resulting from NO-induced conversion of XO to its relatively inactive desulfo-form. Steady-state kinetic parameters were determined spectrophotometrically for urate production and NADH oxidation catalyzed by XO and xanthine dehydrogenase in the presence of nitrite under anaerobic conditions. pH optima for anaerobic NO production catalyzed by XO in the presence of nitrite were 7.0 for NADH and </=6.0 for xanthine. Involvement of the molybdenum site of XO in nitrite reduction was shown by the fact that alloxanthine inhibits xanthine oxidation competitively with nitrite. Strong preference for Mo=S over Mo=O was shown by the relatively very low NADH-nitrite reductase activity shown by desulfo-enzyme. The FAD site of XO was shown not to influence nitrite reduction in the presence of xanthine, although it was clearly involved when NADH was the reducing substrate. Apparent production of NO decreased with increasing oxygen tensions, consistent with reaction of NO with XO-generated superoxide. It is proposed that XO-derived NO fulfills a bactericidal role in the digestive tract.

Age-dependent increase of heme oxygenase-1 gene expression in the liver mediated by NFkappaB

Heme, the iron-porphyrin coordination complex, released from the degradation of hemoproteins, is a strong prooxidant. It is enzymatically degraded by heme oxygenase to free iron, carbon monoxide and biliverdin. Biliverdin and its reduced metabolite bilirubin are two potent physiological antioxidants. Here we show a progressive increase of steady-state levels of the mRNA encoding the inducible isoform of this enzyme (heme oxygenase-1) in the rat liver during aging. We had previously reported that aging is associated with increased activation of the nuclear factor kappaB (NFkappaB). We now provide evidence to establish that overexpression of NFkappaB in transfected liver-derived HepG2 cells can cause a marked induction of the endogenous heme oxygenase-1 (HO-1) mRNA and activation of the cotransfected HO-1 gene promoter. Taken together, these results support the conclusion that enhanced oxidative stress during aging is accompanied by compensatory induction of the antioxidant enzyme HO-1 through activation of the NFkappaB pathway.

A review and proposed nomenclature for major proteins of the milk-fat globule membrane

The characteristics and possible functions of the most abundant proteins associated with the bovine milk-fat globule membrane are reviewed. Under the auspices of the Milk Protein Nomenclature Committee of the ADSA, a revised nomenclature for the major membrane proteins is proposed and discussed in relation to earlier schemes. We recommend that proteins be assigned specific names as they are identified by molecular cloning and sequencing techniques. The practice of identifying proteins according to their Mr, electrophoretic mobility, or staining characteristics should be discontinued, except for uncharacterized proteins. The properties and amino acid sequences of the following proteins are discussed in detail: MUC1, xanthine dehydrogenase/oxidase, CD36, butyrophilin, adipophilin, periodic acid Schiff 6/7 (PAS 6/7), and fatty acid binding protein. In addition, a compilation of less abundant proteins associated with the bovine milk-fat globule membrane is presented.

Adhesion and pollution particle-induced oxidant generation is neither necessary nor sufficient for cytokine induction in human alveolar macrophages

Adhesion of human monocytes (MOs) results in the rapid transcriptional activation of cytokine genes that are dependent on nuclear factor (NF)-kappaB. Several pathways leading to activation of NF-kappaB have been described, including those involving reactive oxygen intermediates (ROIs) and members of the mitogen-activated protein (MAP) kinase superfamily. To investigate the involvement of tyrosine phosphorylation (TP) and oxidant generation in interleukin (IL)-8 and GRO messenger RNA induction, MOs and human alveolar macrophages (AMs) were adhered to plastic or exposed to a particulate pollutant, residual oil fly ash (ROFA). Both stimuli caused rapid TP and ROI production in MOs and AMs. However, neither NF-kappaB translocation nor IL-8 gene induction occurred in adhered or ROFA-exposed AMs. Analysis of MAP kinase activation found phosphorylation of Jun amino-terminal kinase (JNK) and p38 in the AMs, but not of extracellular regulated kinase/MAP kinase (ERK/MAPK). AMs stimulated with lipopolysaccharide activated ERK/MAPK, in addition to JNK and p38, and showed translocation of NF-kappaB. In contrast to AMs, MO adhesion or exposure to ROFA particles in suspension rapidly activated p38, JNK, and ERK/MAPK, and activated NF-kappaB binding as well as IL-8 mRNA expression. Pretreatment with the tyrosine kinase inhibitors genistein or herbimycin A before adherence had no effect on transcriptional activation in MOs, whereas adherence and ROFA-induced oxidant generation was inhibited in both MOs and AMs. Taken together, these data indicate that NF-kappaB activation or generalized transcriptional activation of cytokine genes are independent of changes in oxidant stress imposed on phagocytes by adhesion. Furthermore, the data suggest that certain environmental responses in AMs may be uncoupled from activation of NF-kappaB.

Reactive oxygen species and reactive nitrogen species: relevance to cyto(neuro)toxic events and neurologic disorders. An overview

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are formed under physiological conditions in the human body and are removed by cellular antioxidant defense system. During oxidative stress their increased formation leads to tissue damage and cell death. This process may be especially important in the central nervous system (CNS) which is vulnerable to ROS and RNS damage as the result of the brain high O(2) consumption, high lipid content and the relatively low antioxidant defenses in brain, compared with other tissues. Recently there has been an increased number of reports suggesting the involvement of free radicals and their non-radical derivatives in a variety of pathological events and multistage disorders including neurotoxicity, apoptotic death of neurons and neural disorders: Alzheimer's (AD), Parkinson's disease (PD) and schizophrenia. Taking into consideration the basic molecular chemistry of ROS and RNS, their overall generation and location, in order to control or suppress their action it is essential to understand the fundamental aspects of this problem. In this presentation we review and summarize the basics of all the recently known and important properties, mechanisms, molecular targets, possible involvement in cellular (neural) degeneration and apoptotic death and in pathogenesis of AD, PD and schizophrenia. The aim of this article is to provide an overview of our current knowledge of this problem and to inspire experimental strategies for the evaluation of optimum innovative therapeutic trials. Another purpose of this work is to shed some light on one of the most exciting recent advances in our understanding of the CNS: the realisation that RNS pathway is highly relevant to normal brain metabolism and to neurologic disorders as well. The interactions of RNS and ROS, their interconversions and the ratio of RNS/ROS could be an important neural tissue injury mechanism(s) involved into etiology and pathogenesis of AD, PD and schizophrenia. It might be possible to direct therapeutic efforts at oxidative events in the pathway of neuron degeneration and apoptotic death. From reviewed data, no single substance can be recommended for use in human studies. Some of the recent therapeutic strategies and neuroprotective trials need further development particularly those of antioxidants enhancement. Such an approach should also consider using combinations of radical(s) scavengers rather than a single substance.

The importance of being r: greater oxidative stability of RNA compared with DNA

The 2'-hydroxyl group of ribose imparts hydrolytic lability on RNA, which provides a mechanism for numerous biological functions. Recent evidence from chemical cleavage studies shows that this hydroxyl group also stabilizes the sugar moiety in RNA towards oxidation relative to DNA. Is this just because RNA needs to be distinguishable from DNA or does it have other evolutionary significance?

Oxygen stress increases prolyl cis/trans isomerase activity and expression of cyclophilin 18 in rabbit blastocysts

The peptidyl-prolyl cis/trans isomerase (PPIase) activity and the expression of cyclophilins were studied in 6-day-old rabbit preimplantation embryos cultured under physiological and increased oxygen concentrations of 5% and 20% O(2), respectively. The PPIase activity was completely inhibited by cyclosporin A (CsA). The inhibitor of FK506-binding proteins, rapamycin, had no effect on the PPIase activity, indicating that the PPIase activity in rabbit blastocysts originates from cyclophilins. Using CsA affinity chromatography, only one cyclophilin with a molecular mass of about 17.8 kDa was separated. The cDNA of rabbit cyclophilin was cloned and sequenced. Analysis of the 682-base pair cDNA revealed an open reading frame coding for a polypeptide of 164 amino acid residues with a molecular weight of 17.83 kDa. Homologies of 90% and 96% for the cDNA and amino acid sequence, respectively, to the human CyP18 were found, suggesting that the novel rabbit cyclophilin is a member of the CyP18 family (rabCyP18). The transcription level of rabCyP18 mRNA was 8.3 +/- 0.6 pg in 100 ng total RNA in noncultured blastocysts. In vitro culture with moderate oxygen stress (20% O(2)) resulted in a 1.5-fold increase in rabCyP18 transcription and an increased PPIase activity compared to that of blastocysts cultured with 5% O(2). Increase in transcription rate and PPIase activity by oxygen stress suggests an involvement of CyP18 in oxygen defense in rabbit preimplantation embryos.

Nuclear Factor-κB–Dependent Induction of Interleukin-8 Gene Expression by Tumor Necrosis Factor : Evidence for an Antioxidant Sensitive Activating Pathway Distinct From Nuclear Translocation

Tumor necrosis factor  (TNF) is a pluripotent activator of inflammation by inducing a proinflammatory cytokine cascade. This phenomenon is mediated, in part, through inducible expression of the CXC chemokine, interleukin-8 (IL-8). In this study, we investigate the role of TNF-inducible reactive oxygen species (ROS) in IL-8 expression by “monocyte-like” U937 histiocytic lymphoma cells. TNF is a rapid activator of IL-8 gene expression by U937, producing a 50-fold induction of mRNA within 1 hour of treatment. In gene transfection assays, the effect of TNF requires the presence of an inducible nuclear factor-κB (NF-κB) (Rel A) binding site in the IL-8 promoter. TNF treatment induces a rapid translocation of the 65 kD transcriptional activator NF-κB subunit, Rel A, whose binding in the nucleus occurs before changes in intracellular ROS. Pretreatment (or up to 15 minutes posttreatment) relative to TNF with the antioxidant dimethyl sulfoxide (DMSO) (2% [vol/vol]) blocks 80% of NF-κB–dependent transcription. Surprisingly, however, DMSO has no effect on inducible Rel A binding. Similar selective effects on NF-κB transcription are seen with the unrelated antioxidants, N-acetylcysteine (NAC) and vitamin C. These data indicate that TNF induces a delayed ROS-dependent signalling pathway that is required for NF-κB transcriptional activation and is separable from that required for its nuclear translocation. Further definition of this pathway will yield new insights into inflammation initiated by TNF signalling.

Nuclear Factor-κB–Dependent Induction of Interleukin-8 Gene Expression by Tumor Necrosis Factor : Evidence for an Antioxidant Sensitive Activating Pathway Distinct From Nuclear Translocation

Tumor necrosis factor  (TNF) is a pluripotent activator of inflammation by inducing a proinflammatory cytokine cascade. This phenomenon is mediated, in part, through inducible expression of the CXC chemokine, interleukin-8 (IL-8). In this study, we investigate the role of TNF-inducible reactive oxygen species (ROS) in IL-8 expression by “monocyte-like” U937 histiocytic lymphoma cells. TNF is a rapid activator of IL-8 gene expression by U937, producing a 50-fold induction of mRNA within 1 hour of treatment. In gene transfection assays, the effect of TNF requires the presence of an inducible nuclear factor-κB (NF-κB) (Rel A) binding site in the IL-8 promoter. TNF treatment induces a rapid translocation of the 65 kD transcriptional activator NF-κB subunit, Rel A, whose binding in the nucleus occurs before changes in intracellular ROS. Pretreatment (or up to 15 minutes posttreatment) relative to TNF with the antioxidant dimethyl sulfoxide (DMSO) (2% [vol/vol]) blocks 80% of NF-κB–dependent transcription. Surprisingly, however, DMSO has no effect on inducible Rel A binding. Similar selective effects on NF-κB transcription are seen with the unrelated antioxidants, N-acetylcysteine (NAC) and vitamin C. These data indicate that TNF induces a delayed ROS-dependent signalling pathway that is required for NF-κB transcriptional activation and is separable from that required for its nuclear translocation. Further definition of this pathway will yield new insights into inflammation initiated by TNF signalling.

Nuclear translocation of nuclear factor kappa B in early 1-cell mouse embryos

Nuclear factor kappa B (NF-kappaB) is a transcription factor that controls the expression of a number of genes under cellular redox potential. It has recently been found that NF-kappaB plays a pivotal role in morphogenesis and embryonic development, e.g., in formation of Drosophila malanogaster ventral structures and chicken limb buds. However, the role of NF-kappaB in preimplantation development in mammals is not yet understood. In this study, we show that RelA, one of the subunits of NF-kappaB, is expressed in mouse eggs and embryos from the metaphase II (MII) oocyte to the blastocyst stage. Therefore, it is thought that RelA is maternally expressed and that it continues to be expressed during preimplantation development. Immunofluorescence analysis showed that RelA protein was mainly distributed in the cytoplasm of embryos, whereas nuclear translocation of RelA, evidence for NF-kappaB activation, was observed only at the early 1-cell stage. Finally we studied the effects of NF-kappaB inhibitors, pyrrolidine dithiocarbamate and N-acetyl-L-cysteine, on the preimplantation development of mouse embryos. When these inhibitors were added to the culture medium from the early 1-cell stage, subsequent development through the 2-cell stage was inhibited. However, little, if any, influence on the progression through the 2-cell stage was observed when the inhibitors were added at the late 1-cell or the 2-cell stage. Taken together, the results suggest that the activation of NF-kappaB at the early 1-cell stage is required for the development of mouse embryos beyond the 2-cell stage.

Design, synthesis, and evaluation of N-aroyloxy-2-thiopyridones as DNA photocleaving reagents

N-Benzoyloxy-2-thiopyridone (12) was shown to induce single-strand nicks in duplex DNA upon irradiation with visible light (lambda&350 nm). This finding led to the design of a series of compounds, in which an acridinyl nucleus was covalently linked to the N-benzoyloxy-2-thiopyridone unit. These conjugates (15, 16, 17 and 18) were synthesized and evaluated as novel DNA photocleaving reagents. Optimal photocleaving activity was observed for conjugate 16, in which a flexible polymethylene spacer of 4 carbons was used to connect the aminoacridine entity to the thiopyridone. This compound was shown to cleave DNA at low microM concentrations and was approximately two-orders of magnitude more efficient than the parent N-benzoyloxy-2-thiopyridone (12). Furthermore, the DNA cleavage ladders induced by 16 and 12 were found to be identical and of no significant sequence selectivity. These data suggest that the N-aroyloxy-2-thiopyridones can be used for the design of new DNA photocleaving reagents with potential use as 'photofootprinting agents' or as 'site-directed photonucleases'.

Effects of pro- and antioxidative compounds on renal production of erythropoietin

The most important stimulus for the enhanced synthesis of erythropoietin (Epo) is a lowered O2 tension in the tissue. However, the mechanism by which an impaired O2 supply is transduced into appropriate Epo production is still not fully understood. Recently, studies in human hepatoma cells (line HepG2) indicate that reactive O2 species are involved in the signal transduction from the cellular O2 sensor to the Epo gene. To clarify the role of reactive O2 species in the regulation of Epo synthesis in the kidney, the principal Epo-producing organ in vivo, we investigated the influence of potent pro- and antioxidants on Epo production in isolated perfused rat kidneys. Under normoxic conditions, the iron chelator desferrioxamine and the antioxidant vitamin A increased renal Epo production, mimicking hypoxic induction. In contrast, supplementation of the perfusion medium of hypoxically perfused kidneys with the prooxidant compounds H2O2 or pyrogallol caused a significant reduction of Epo synthesis. The inhibition of Epo formation by reactive O2 species could be completely antagonized by desferrioxamine and the hydroxyl radical-(OH*)-scavenger tetramethylthiourea. Vitamin A also antagonized the H2O2-dependent inhibition of hypoxically induced Epo synthesis. Interestingly, the addition of the antioxidant vitamin A to hypoxically perfused kidneys also induced Epo production significantly. Our data strongly support the idea that reactive O2 species, especially H2O2, are part of the signaling chain of the cellular O2-sensing mechanism regulating the renal synthesis of Epo.

Bioluminescence

Bioluminescence has evolved independently many times; thus the responsible genes are unrelated in bacteria, unicellular algae, coelenterates, beetles, fishes, and others. Chemically, all involve exergonic reactions of molecular oxygen with different substrates (luciferins) and enzymes (luciferases), resulting in photons of visible light (approximately 50 kcal). In addition to the structure of luciferan, several factors determine the color of the emissions, such as the amino acid sequence of the luciferase (as in beetles, for example) or the presence of accessory proteins, notably GFP, discovered in coelenterates and now used as a reporter of gene expression and a cellular marker. The mechanisms used to control the intensity and kinetics of luminescence, often emitted as flashes, also vary. Bioluminescence is credited with the discovery of how some bacteria, luminous or not, sense their density and regulate specific genes by chemical communication, as in the fascinating example of symbiosis between luminous bacteria and squid.

Oxidative stress in microorganisms--I. Microbial vs. higher cells--damage and defenses in relation to cell aging and death

Oxidative stress in microbial cells shares many similarities with other cell types but it has its specific features which may differ in prokaryotic and eukaryotic cells. We survey here the properties and actions of primary sources of oxidative stress, the role of transition metals in oxidative stress and cell protective machinery of microbial cells, and compare them with analogous features of other cell types. Other features to be compared are the action of Reactive Oxygen Species (ROS) on cell constituents, secondary lipid- or protein-based radicals and other stress products. Repair of oxidative injury by microorganisms and proteolytic removal of irreparable cell constituents are briefly described. Oxidative damage of aerobically growing microbial cells by endogenously formed ROS mostly does not induce changes similar to the aging of multiplying mammalian cells. Rapid growth of bacteria and yeast prevents accumulation of impaired macromolecules which are repaired, diluted or eliminated. During growth some simple fungi, such as yeast or Podospora spp., exhibit aging whose primary cause seems to be fragmentation of the nucleolus or impairment of mitochondrial DNA integrity. Yeast cell aging seems to be accelerated by endogenous oxidative stress. Unlike most growing microbial cells, stationary-phase cells gradually lose their viability because of a continuous oxidative stress, in spite of an increased synthesis of antioxidant enzymes. Unlike in most microorganisms, in plant and animal cells a severe oxidative stress induces a specific programmed death pathway--apoptosis. The scant data on the microbial death mechanisms induced by oxidative stress indicate that in bacteria cell death can result from activation of autolytic enzymes (similarly to the programmed mother-cell death at the end of bacillary sporulation). Yeast and other simple eukaryotes contain components of a proapoptotic pathway which are silent under normal conditions but can be activated by oxidative stress or by manifestation of mammalian death genes, such as bak or bax. Other aspects, such as regulation of oxidative-stress response, role of defense enzymes and their control, acquisition of stress tolerance, stress signaling and its role in stress response, as well as cross-talk between different stress factors, will be the subject of a subsequent review.