Diphenyleneiodonium inhibits reduction of iron-sulfur clusters in the mitochondrial NADH-ubiquinone oxidoreductase (Complex I)

Resveratrol blocks Akt activation in angiotensin II- or EGF-stimulated vascular smooth muscle cells in a redox-independent manner

Aims

Resveratrol (RV), an antioxidant, inhibits angiotensin II (Ang II)-induced hypertrophy and Ang II- or epidermal growth factor (EGF)-induced Akt phosphorylation in rat vascular smooth muscle cells (VSMCs). Both signalling pathways are reported to utilize reactive oxygen species (ROS). The aim of this study was to show whether RV reduces the ROS level in Ang II- or EGF-activated VSMCs and whether reduction of ROS causes the impeded signalling towards Akt in the presence of RV.

Methods and results

We show here that RV reduces intracellular ROS and extracellular H₂O₂ release from VSMCs as measured using 2′,7′-dichlorodihydrofluorescein-diacetate and Amplex Red™. Since NADPH oxidases (Nox) 1 and 4 are major ROS sources in VSMCs, we examined their need for Akt phosphorylation in response to Ang II or EGF. Experiments using the blocking peptide gp91ds-tat verified a role for Nox1 in Ang II signalling towards Akt, but excluded a role for Nox1 in the respective EGF signalling. A small interfering RNA-mediated knock-down of Nox4 showed that Nox4 was not required for Ang II- or EGF-induced Akt phosphorylation. Use of the flavoprotein inhibitor diphenyleneiodonium, N-acetyl-cysteine, and non-antioxidant RV derivatives revealed that the antioxidant capacity of RV is not required for the inhibition of Akt phosphorylation, in both rat and human VSMCs.

Conclusion

Thus, although RV acts as an antioxidant, the antihypertrophic response of RV in VSMCs and the signalling downstream of the EGF receptor towards Akt seem to be largely redox independent.

Mitochondrial redox potential during contraction in single intact muscle fibers

Although the production of reactive oxygen species (ROS) during muscle contractile activity has been linked to both positive and negative adaptive responses, the sites for ROS generation within working muscle are not clearly defined. We assessed cytosolic ROS production and mitochondrial redox potential with a targeted redox-sensitive green fluorescent protein during repetitive field stimulation of single mature myofibers. Cytosolic ROS production increased by 94%, an effect that was abolished by pretreatment with the reducing agent dithiothreitol. Mitochondrial redox potential was not altered during muscle contraction. In contrast, activity-dependent ROS production was ablated by an inhibitor of NADPH oxidase. We provide the first report on dynamic ROS production from mitochondria in single living myofibers and suggest that the mitochondria are not the major source of ROS during skeletal muscle contraction. Alternatively, our data support a role for NADPH oxidase-derived ROS during contractile activity.

Bacterial Na+-translocating ferredoxin:NAD+ oxidoreductase

The anaerobic acetogenic bacterium Acetobacterium woodii carries out a unique type of Na(+)-motive, anaerobic respiration with caffeate as electron acceptor, termed "caffeate respiration." Central, and so far the only identified membrane-bound reaction in this respiration pathway, is a ferredoxin:NAD(+) oxidoreductase (Fno) activity. Here we show that inverted membrane vesicles of A. woodii couple electron transfer from reduced ferredoxin to NAD(+) with the transport of Na(+) from the outside into the lumen of the vesicles. Na(+) transport was electrogenic, and accumulation was inhibited by sodium ionophores but not protonophores, demonstrating a direct coupling of Fno activity to Na(+) transport. Results from inhibitor studies are consistent with the hypothesis that Fno activity coupled to Na(+) translocation is catalyzed by the Rnf complex, a membrane-bound, iron-sulfur and flavin-containing electron transport complex encoded by many bacterial and some archaeal genomes. Fno is a unique type of primary Na(+) pump and represents an early evolutionary mechanism of energy conservation that expands the redox range known to support life. In addition, it explains the lifestyle of many anaerobic bacteria and gives a mechanistic explanation for the enigma of the energetic driving force for the endergonic reduction of ferredoxin with NADH plus H(+) as reductant in a number of aerobic bacteria.

Co-occurring increases of calcium and organellar reactive oxygen species determine differential activation of antioxidant and defense enzymes in Ulva compressa (Chlorophyta) exposed to copper excess

In order to analyse copper-induced calcium release and (reactive oxygen species) ROS accumulation and their role in antioxidant and defense enzymes activation, the marine alga Ulva compressa was exposed to 10 µM copper for 7 d. The level of calcium, extracellular hydrogen peroxide (eHP), intracellular hydrogen peroxide (iHP) and superoxide anions (SA) as well as the activities of ascorbate peroxidase (AP), glutathione reductase (GR), glutathione-S-transferase (GST), phenylalanine ammonia lyase (PAL) and lipoxygenase (LOX) were determined. Calcium release showed a triphasic pattern with peaks at 2, 3 and 12 h. The second peak was coincident with increases in eHP and iHP and the third peak with the second increase of iHP. A delayed wave of SA occurred after day 3 and was not accompanied by calcium release. The accumulation of iHP and SA was mainly inhibited by organellar electron transport chains inhibitors (OETCI), whereas calcium release was inhibited by ryanodine. AP activation ceased almost completely after the use of OETCI. On the other hand, GR and GST activities were partially inhibited, whereas defense enzymes were not inhibited. In contrast, PAL and LOX were inhibited by ryanodine, whereas AP was not inhibited. Thus, copper stress induces calcium release and organellar ROS accumulation that determine the differential activation of antioxidant and defense enzymes.

Redox signaling and reactive oxygen species in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an essential physiological mechanism of the lung that matches blood perfusion with alveolar ventilation to optimize gas exchange. Perturbations of HPV, as may occur in pneumonia or adult respiratory distress syndrome, can cause life-threatening hypoxemia. Despite intensive research for decades, the molecular mechanisms of HPV have not been fully elucidated. Reactive oxygen species (ROS) and changes in the cellular redox state are proposed to link O2 sensing and pulmonary arterial smooth muscle cell contraction underlying HPV. In this regard, mitochondria and NAD(P)H oxidases are discussed as sources of ROS. However, there is controversy whether ROS levels decrease or increase during hypoxia. With this background we summarize the current knowledge on the role of ROS and redox state in HPV.

Hypoxia-induced changes in pulmonary and systemic vascular resistance: where is the O2 sensor?

Pulmonary arteries (PA) constrict in response to alveolar hypoxia, whereas systemic arteries (SA) undergo dilation. These physiological responses reflect the need to improve gas exchange in the lung, and to enhance the delivery of blood to hypoxic systemic tissues. An important unresolved question relates to the underlying mechanism by which the vascular cells detect a decrease in oxygen tension and translate that into a signal that triggers the functional response. A growing body of work implicates the mitochondria, which appear to function as O2 sensors by initiating a redox-signaling pathway that leads to the activation of downstream effectors that regulate vascular tone. However, the direction of this redox signal has been the subject of controversy. Part of the problem has been the lack of appropriate tools to assess redox signaling in live cells. Recent advancements in the development of redox sensors have led to studies that help to clarify the nature of the hypoxia-induced redox signaling by reactive oxygen species (ROS). Moreover, these studies provide valuable insight regarding the basis for discrepancies in earlier studies of the hypoxia-induced mechanism of redox signaling. Based on recent work, it appears that the O2 sensing mechanism in both the PA and SA are identical, that mitochondria function as the site of O2 sensing, and that increased ROS release from these organelles leads to the activation of cell-specific, downstream vascular responses.

Qo site of mitochondrial complex III is the source of increased superoxide after transient exposure to hydrogen peroxide

Transient exposure of cardiac myocytes to hydrogen peroxide (H(2)O(2)) results in further production of superoxide by the mitochondria as a result of increased influx of calcium through the L-type Ca(2+) channel and increased calcium uptake by the mitochondria. The response persists as a result of positive feedback on the channel and induces alterations in protein synthesis and cell size consistent with the development of myocyte hypertrophy. The aim of this study was to investigate the site of increased superoxide production within the mitochondria. Exposure of myocytes to 30 μM H(2)O(2) (5 min) then 10 U/mL catalase (5 min) increased dihydroethidium (DHE) signal by 58.7 ± 12.0% (n=4) compared to myocytes exposed to 0 μM H(2)O(2) for 5 min followed by 10 U/mL catalase (n=9). Complex I inhibitors DPI (n=5) and rotenone (n=7) attenuated the increase in DHE signal due to H(2)O(2). Complex III inhibitors myxothiazol (n=16) and stigmatellin (n=5) also attenuated the increase in DHE signal due to H(2)O(2). However, antimycin A (inhibitor of Q(i) site of complex III) had no effect. We "isolated" complex III in the intact cell by applying succinate in the patch pipette and exposing the cell to rotenone and antimycin A. Myxothiazol and TCA cycle inhibitors α-keto-β-methyl-n-valeric acid (KMV) and 4-hydroxynonenal (4-HNE) completely attenuated the increase in DHE signal. Direct activation of the L-type Ca(2+) channel by voltage-step mimicked the increase in DHE signal after transient exposure to H(2)O(2) (47.6 ± 17.8%, n=6) while intracellular application of catalase attenuated the increase in DHE signal due to H(2)O(2) (n=6). We propose that elevated superoxide production after transient exposure to H(2)O(2) occurs at the Q(o) superoxide generation site of complex III in cardiac myocytes and that an increase in TCA cycle activity plays a significant role in mediating the response.

Comparison of in vivo postexercise phosphocreatine recovery and resting ATP synthesis flux for the assessment of skeletal muscle mitochondrial function

(31)P magnetic resonance spectroscopy (MRS) has been used to assess skeletal muscle mitochondrial function in vivo by measuring 1) phosphocreatine (PCr) recovery after exercise or 2) resting ATP synthesis flux with saturation transfer (ST). In this study, we compared both parameters in a rat model of mitochondrial dysfunction with the aim of establishing the most appropriate method for the assessment of in vivo muscle mitochondrial function. Mitochondrial dysfunction was induced in adult Wistar rats by daily subcutaneous injections with the complex I inhibitor diphenyleneiodonium (DPI) for 2 wk. In vivo (31)P MRS measurements were supplemented by in vitro measurements of oxygen consumption in isolated mitochondria. Two weeks of DPI treatment induced mitochondrial dysfunction, as evidenced by a 20% lower maximal ADP-stimulated oxygen consumption rate in isolated mitochondria from DPI-treated rats oxidizing pyruvate plus malate. This was paralleled by a 46% decrease in in vivo oxidative capacity, determined from postexercise PCr recovery. Interestingly, no significant difference in resting, ST-based ATP synthesis flux was observed between DPI-treated rats and controls. These results show that PCr recovery after exercise has a more direct relationship with skeletal muscle mitochondrial function than the ATP synthesis flux measured with (31)P ST MRS in the resting state.

Rotenone enhances the antifungal properties of staurosporine

We studied staurosporine-induced cell death in the filamentous fungus Neurospora crassa. The generation of reactive oxygen species during the process appears to be an important signaling event, since addition of the antioxidant glutathione prevents the effects of staurosporine on fungal growth. Selected mutants with mutations in respiratory chain complex I are extremely sensitive to the drug, stressing the involvement of complex I in programmed cell death. Following this finding, we determined that the complex I-specific inhibitor rotenone used in combination with staurosporine results in a synergistic and specific antifungal activity, likely through a concerted action on intracellular glutathione depletion. Paradoxically, the synergistic antifungal activity of rotenone and staurosporine is observed in N. crassa complex I mutants and in Saccharomyces cerevisiae, which lacks complex I. In addition, it is not observed when other complex I inhibitors are used instead of rotenone. These results indicate that the rotenone effect is independent of complex I inhibition. The combination of rotenone and staurosporine is effective against N. crassa as well as against the common pathogens Aspergillus fumigatus and Candida albicans, pointing to its usefulness as an antifungal agent.

TRPM7 activates m-calpain by stress-dependent stimulation of p38 MAPK and c-Jun N-terminal kinase

TRPM7 is a Ca(2)(+)-permeant and Mg(2)(+)-permeant ion channel in possession of its own kinase domain. In a previous study, we showed that overexpression of the channel-kinase in HEK-293 cells produced cell rounding and loss of adhesion, which was dependent on the Ca(2+)-dependent protease m-calpain. The TRPM7-elicited change in cell morphology was channel-dependent and occurred without any significant increase in cytosolic Ca(2+). Here we demonstrate that overexpression of TRPM7 increased levels of cellular reactive oxygen species (ROS) and nitric oxide, causing the activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK). Application of inhibitors of p38 MAPK and JNK blocked TRPM7-induced cell rounding and activation of m-calpain, without affecting the phosphorylation state of the protease. Overexpression of TRPM7 increased intracellular Mg(2+); however, when the concentration of either external Ca(2+) or Mg(2+) was increased to favor the permeation of one divalent cation over the other, a similar increase in cell rounding and calpain activity was detected, indicating that TRPM7-mediated activation of m-calpain is not dependent on the nature of the divalent conducted by the channel. Application of inhibitors of nitric oxide synthase and mitochondrial-derived ROS reduced TRPM7-induced increases in nitric oxide and ROS production, blocked the change in cell morphology, and reduced cellular calpain activity. Collectively, our data reveal that excessive TRPM7 channel activity causes oxidative and nitrosative stresses, producing cell rounding mediated by p38 MAPK/JNK-dependent activation of m-calpain.

Towards the molecular mechanism of respiratory complex I

Complex I (NADH:quinone oxidoreductase) is crucial to respiration in many aerobic organisms. In mitochondria, it oxidizes NADH (to regenerate NAD+ for the tricarboxylic acid cycle and fatty-acid oxidation), reduces ubiquinone (the electrons are ultimately used to reduce oxygen to water) and transports protons across the mitochondrial inner membrane (to produce and sustain the protonmotive force that supports ATP synthesis and transport processes). Complex I is also a major contributor to reactive oxygen species production in the cell. Understanding the mechanisms of energy transduction and reactive oxygen species production by complex I is not only a significant intellectual challenge, but also a prerequisite for understanding the roles of complex I in disease, and for the development of effective therapies. One approach to defining a complicated reaction mechanism is to break it down into manageable parts that can be tackled individually, before being recombined and integrated to produce the complete picture. Thus energy transduction by complex I comprises NADH oxidation by a flavin mononucleotide, intramolecular electron transfer from the flavin to bound quinone along a chain of iron–sulfur clusters, quinone reduction and proton translocation. More simply, molecular oxygen is reduced by the flavin, to form the reactive oxygen species superoxide and hydrogen peroxide. The present review summarizes and evaluates experimental data that pertain to the reaction mechanisms of complex I, and describes and discusses contemporary mechanistic hypotheses, proposals and models.

Telomeric DNA induces p53-dependent reactive oxygen species and protects against oxidative damage

BACKGROUND

Reactive oxygen species (ROS) are generated by cellular metabolism as well as by exogenous agents. While ROS can promote cellular senescence, they can also act as signaling molecules for processes that do not lead to senescence. Telomere homolog oligonucleotides (T-oligos) induce adaptive DNA damage responses including increased DNA repair capacity and these effects are mediated, at least in part, through p53.

OBJECTIVE

Studies were undertaken to determine whether such p53-mediated protective responses include enhanced antioxidant defenses.

METHODS

Normal human fibroblasts as well as R2F fibroblasts expressing wild type or dominant negative p53 were treated with an 11-base T-oligo, a complementary control oligo or diluents alone and then examined by western blot analysis, immunofluorescence microscopy and various biochemical assays.

RESULTS

We now report that T-oligo increases the level of the antioxidant enzymes superoxide dismutase 1 and 2 and protects cells from oxidative damage; and that telomere-based gammaH2AX (DNA damage) foci that form in response to T-oligos contain phosphorylated ATM and Chk2, proteins known to activate p53 and to mediate cell cycle arrest in response to oxidative stress. Further, T-oligo increases cellular ROS levels via a p53-dependent pathway, and these increases are abrogated by the NAD(P)H oxidase inhibitor diphenyliodonium chloride.

CONCLUSION

These results suggest the existence of innate telomere-based protective responses that act to reduce oxidative damage to cells. T-oligo treatment induces the same responses and offers a new model for studying intracellular ROS signaling and the relationships between DNA damage, ROS, oxidative stress, and cellular defense mechanisms.

The NADPH oxidase inhibitor diphenyleneiodonium is also a potent inhibitor of cholinesterases and the internal Ca(2+) pump

BACKGROUND AND PURPOSE

Diphenyleneiodonium (DPI) is often used as an NADPH oxidase inhibitor, but is increasingly being found to have unrelated side effects. We investigated its effects on smooth muscle contractions and the related mechanisms.

EXPERIMENTAL APPROACH

We studied isometric contractions in smooth muscle strips from bovine trachea. Cholinesterase activity was measured using a spectrophotometric assay; internal Ca(2+) pump activity was assessed by Ca(2+) uptake into smooth muscle microsomes.

KEY RESULTS

Contractions to acetylcholine were markedly enhanced by DPI (10(-4) M), whereas those to carbachol (CCh) were not, suggesting a possible inhibition of cholinesterase. DPI markedly suppressed contractions evoked by CCh, KCl and 5-HT, and also unmasked phasic activity in otherwise sustained responses. Direct biochemical assays confirmed that DPI was a potent inhibitor of acetylcholinesterase and butyrylcholinesterase (IC(50) approximately 8 x 10(-6) M and 6 x 10(-7) M, respectively), following a readily reversible, mixed non-competitive type of inhibition. The inhibitory effects of DPI on CCh contractions were not mimicked by another NADPH oxidase inhibitor (apocynin), nor the Src inhibitors PP1 or PP2, ruling out an action through the NADPH oxidase signalling pathway. Several features of the DPI-mediated suppression of agonist-evoked responses (i.e. suppression of peak magnitudes and unmasking of phasic activity) are similar to those of cyclopiazonic acid, an inhibitor of the internal Ca(2+) pump. Direct measurement of microsomal Ca(2+) uptake revealed that DPI modestly inhibits the internal Ca(2+) pump.

CONCLUSIONS AND IMPLICATIONS

DPI inhibits cholinesterase activity and the internal Ca(2+) pump in tracheal smooth muscle.

On the mechanism of apoplastic H2O2 production during lignin formation and elicitation in cultured spruce cells--peroxidases after elicitation

A cell culture of Picea abies (L.) Karst. was used for studies of H(2)O(2) generation during constitutive extracellular lignin formation and after elicitation by cell wall fragments of a pathogenic fungus, Heterobasidium parviporum. Stable, micromolar levels of H(2)O(2) were present in the culture medium during lignin formation. Elicitation induced a burst of H(2)O(2), peaking at ca. 90 min after elicitation. Of exogenous reducing substrates that may be responsible for the synthesis of H(2)O(2) from O(2), NADH stimulated H(2)O(2) production irrespective of elicitation. Cysteine (Cys) and glutathione (GSH) partially scavenged the constitutive H(2)O(2), but usually increased or prolonged elicitor-induced H(2)O(2) formation. Culture medium peroxidases were not able to generate H(2)O(2) in vitro with Cys or GSH as reductants. These thiols, however, generated H(2)O(2) non-enzymically at pH 4.5. [(35)S]Sulphate feeding to spruce cells showed that endogenous sulphur-containing compounds (including GSH, GSSG and cysteic acid) existed in the culture medium. The apoplastic levels of these were, however, undetectable by the monobromobimane method suggesting that their contribution to apoplastic H(2)O(2) formation is probably minor. Azide, an inhibitor of haem-containing enzymes, slightly inhibited constitutive H(2)O(2) generation but strongly delayed the elicitor-induced H(2)O(2) accumulation. Diphenylene iodonium, an inhibitor of flavin-containing enzymes, efficiently inhibited H(2)O(2) production irrespective of elicitation. Elicitation led to downregulation of the expression of several peroxidase genes, and peroxidase activity in the culture medium was slightly reduced. Expression of three other peroxidase genes and a respiratory burst oxidase homologue (rboh) gene were upregulated. These data suggest that both peroxidases and rboh may contribute to H(2)O(2) generation.

Insufficiency of pro-heparin-binding epidermal growth factor-like growth factor shedding enhances hypoxic cell death in H9c2 cardiomyoblasts via the activation of caspase-3 and c-Jun N-terminal kinase

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a cardiogenic and cardiohypertrophic growth factor. ProHB-EGF, a product of the Hb-egf gene and the precursor of HB-EGF, is anchored to the plasma membrane. Its ectodomain region is shed by a disintegrin and metalloproteases (ADAMs) when activated by various stimulations. It has been reported that an uncleavable mutant of Hb-egf, uc-Hb-egf, produces uc-proHB-EGF, which is not cleaved by ADAMs and causes dilation of the heart in knock-in mice. This suggests that the shedding of proHB-EGF is essential for the development and survival of cardiomyocytes: however, the molecular mechanism involved has remained unclear. In this study, we investigated the relationship between uc-proHB-EGF expression and cardiomyocyte survival. Human uc-proHB-EGF was adenovirally introduced into the rat cardiomyoblast cell line H9c2, and the cells were cultured under normoxic and hypoxic conditions. Uc-proHB-EGF-expressing H9c2 cells underwent apoptosis under normoxic conditions, which distinctly increased under hypoxic conditions. Furthermore, we observed an increased Caspase-3 activity, reactive oxygen species accumulation, and an increased c-Jun N-terminal kinase (JNK) activity in the uc-proHB-EGF-expressing H9c2 cells. Treatment of the uc-proHB-EGF transfectants with inhibitors of Caspase-3, reactive oxygen species, and JNK, namely, Z-VAD-fmk, N-acetylcysteine, and SP600125, respectively, significantly reduced hypoxic cell death. These data indicate that insufficiency of proHB-EGF shedding under hypoxic stress leads to cardiomyocyte apoptosis via Caspase-3- and JNK-dependent pathways.

Type II NADH dehydrogenase of the respiratory chain of Plasmodium falciparum and its inhibitors

Plasmodium falciparum NDH2 (pfNDH2) is a non-proton pumping, rotenone-insensitive alternative enzyme to the multi-subunit NADH:ubiquinone oxidoreductases (Complex I) of many other eukaryotes. Recombinantly expressed pfNDH2 prefers coenzyme CoQ(0) as an acceptor substrate, and can also use the artificial electron acceptors, menadione and dichlorophenol-indophenol (DCIP). Previously characterized NDH2 inhibitors, dibenziodolium chloride (DPI), diphenyliodonium chloride (IDP), and 1-hydroxy-2-dodecyl-4(1H)quinolone (HDQ) do not inhibit pfNDH2 activity. Here, we provide evidence that HDQ likely targets another P. falciparum mitochondrial enzyme, dihydroorotate dehydrogenase (pfDHOD), which is essential for de novo pyrimidine biosynthesis.

Differential effects of mitochondrial Complex I inhibitors on production of reactive oxygen species

We have investigated the production of reactive oxygen species (ROS) by Complex I in isolated open bovine heart submitochondrial membrane fragments during forward electron transfer in presence of NADH, by means of the probe 2',7'-Dichlorodihydrofluorescein diacetate. ROS production by Complex I is strictly related to its inhibited state. Our results indicate that different Complex I inhibitors can be grouped into two classes: Class A inhibitors (Rotenone, Piericidin A and Rolliniastatin 1 and 2) increase ROS production; Class B inhibitors (Stigmatellin, Mucidin, Capsaicin and Coenzyme Q(2)) prevent ROS production also in the presence of Class A inhibitors. Addition of the hydrophilic Coenzyme Q(1) as an electron acceptor potentiates the effect of Rotenone-like inhibitors in increasing ROS production, but has no effect in the presence of Stigmatellin-like inhibitors; the effect is not shared by more hydrophobic quinones such as decyl-ubiquinone. This behaviour relates the prooxidant CoQ(1) activity to a hydrophilic electron escape site. Moreover the two classes of Complex I inhibitors have an opposite effect on the increase of NADH-DCIP reduction induced by short chain quinones: only Class B inhibitors allow this increase, indicating the presence of a Rotenone-sensitive but Stigmatellin-insensitive semiquinone species in the active site of the enzyme. The presence of this semiquinone was also suggested by preliminary EPR data. The results suggest that electron transfer from the iron-sulphur clusters (N2) to Coenzyme Q occurs in two steps gated by two different conformations, the former being sensitive to Rotenone and the latter to Stigmatellin.

A key role for redox signaling in rapid P2X7 receptor-induced IL-1 beta processing in human monocytes

P2X(7) receptors (P2X(7)Rs) are ATP-gated ion channels that trigger caspase-1 activation in the presence of TLR ligands. Inflammatory caspase-1 is responsible for the proteolytic activation of IL-1beta. However, the signaling events that couple P2X(7)Rs to caspase-1 activation remain undefined. In this study we demonstrate that ATP-induced cellular oxidation is critical for caspase-1 activation and subsequent IL-1beta processing. Purinergic receptor stimulation, including P2X(7)Rs, of endotoxin-primed human monocytes augments NADPH oxidase activity whereas concurrent purinergic receptor stimulation triggers protein denitroyslation, leading to the formation of peroxynitrite. IL-1beta cleavage is blocked under conditions where superoxide anion formation is blocked or monocytes are treated with antioxidants or a peroxynitrite scavenger. Nigericin, a K(+)/H(+) antiporter, also increases NADPH oxidase activity, leading to IL-1beta and caspase-1 processing that is blocked by a peroxynitrite scavenger or inhibition of NADPH oxidase. These data demonstrate that signaling via NADPH oxidase activity is fundamental for the processing of mature IL-1beta induced by P2X(7)R stimulation.

Mitochondrial NADH fluorescence is enhanced by complex I binding

Mitochondrial NADH fluorescence has been a useful tool in evaluating mitochondrial energetics both in vitro and in vivo. Mitochondrial NADH fluorescence is enhanced several-fold in the matrix through extended fluorescence lifetimes (EFL). However, the actual binding sites responsible for NADH EFL are unknown. We tested the hypothesis that NADH binding to Complex I is a significant source of mitochondrial NADH fluorescence enhancement. To test this hypothesis, the effect of Complex I binding on NADH fluorescence efficiency was evaluated in purified protein, and in native gels of the entire porcine heart mitochondria proteome. To avoid the oxidation of NADH in these preparations, we conducted the binding experiments under anoxic conditions in a specially designed apparatus. Purified intact Complex I enhanced NADH fluorescence in native gels approximately 10-fold. However, no enhancement was detected in denatured individual Complex I subunit proteins. In the Clear and Ghost native gels of the entire mitochondrial proteome, NADH fluorescence enhancement was localized to regions where NADH oxidation occurred in the presence of oxygen. Inhibitor and mass spectroscopy studies revealed that the fluorescence enhancement was specific to Complex I proteins. No fluorescence enhancement was detected for MDH or other dehydrogenases in this assay system, at physiological mole fractions of the matrix proteins. These data suggest that NADH associated with Complex I significantly contributes to the overall mitochondrial NADH fluorescence signal and provides an explanation for the well established close correlation of mitochondrial NADH fluorescence and the metabolic state.

Innervation and activity dependent dynamics of postsynaptic oxidative metabolism

Despite extensive investigations into the mechanisms of aerobic respiration in mitochondria, the spontaneous metabolic activity of individual cells within a whole animal has not been observed in real time. Consequently, little is known about whether and how the level of mitochondrial energy metabolism is regulated in a cell during development of intact systems. Here we studied the dynamics of postsynaptic oxidative metabolism by monitoring the redox state of mitochondrial flavoproteins, an established indicator of energy metabolism, at the developing Drosophila neuromuscular junction. We detected transient and spatially synchronized flavoprotein autofluorescence signals in postsynaptic muscle cells. These signals were dependent on the energy substrates and coupled to changes in mitochondrial membrane potential and Ca2+ concentration. Notably, the rate of autofluorescence signals increased during synapse formation through contact with the motoneuronal axon. This rate was also influenced by the magnitude of synaptic inputs. Thus, presynaptic cells tightly regulate postsynaptic energy metabolism presumably to maintain an energetic balance during neuromuscular synaptogenesis. Our results suggest that flavoprotein autofluorescence imaging should allow us to begin assessing the progress of synapse formation from a metabolic perspective.

Mitochondrial respiratory dysfunction in familiar parkinsonism associated with PINK1 mutation

In the present study mitochondrial respiratory function of fibroblasts from a patient affected by early-onset parkinsonism carrying the homozygous W437X nonsense mutation in the PINK1 gene has been thoroughly characterized. When compared with normal fibroblasts, the patient's fibroblast mitochondria exhibited a lower respiratory activity and a decreased respiratory control ratio with cellular ATP supply relying mainly on enhanced glycolytic production. The quantity, specific activity and subunit pattern of the oxidative phosphorylation complexes were normal. However, a significant decrease of the cellular cytochrome c content was observed and this correlated with a reduced cytochrome c oxidase in situ-activity. Measurement of ROS revealed in mitochondria of the patient's fibroblasts enhanced O(2)(*-) and H(2)O(2) production abrogated by inhibition of complex I. No change in the glutathione-based redox buffering was, however, observed.

Diphenyleneiodonium acutely inhibits reactive oxygen species production by mitochondrial complex I during reverse, but not forward electron transport

We investigated the effects of diphenyleneiodonium (DPI) on superoxide production by complex I in mitochondria isolated from rat skeletal muscle. Superoxide production was measured indirectly as hydrogen peroxide production. In a conventional medium containing chloride, DPI strongly inhibited superoxide production by complex I driven by reverse electron transport from succinate. In principle, this inhibition could be explained by an observed decrease in the mitochondrial pH gradient caused by the known chloride-hydroxide antiport activity of DPI. In a medium containing gluconate instead of chloride, DPI did not affect the pH gradient. In this gluconate medium, DPI still inhibited superoxide production driven by reverse electron transport, showing that the inhibition of superoxide production was not dependent on changes in the pH gradient. It had no effect on superoxide production during forward electron transport from NAD-linked substrates in the presence of rotenone (to maximise superoxide production from the flavin of complex I) or antimycin (to maximise superoxide production from complex III), suggesting that the effects of DPI were not through inhibition of the flavin. We conclude that DPI has the novel and potentially very useful ability to prevent superoxide production from the site in complex I that is active during reverse electron transport, without affecting superoxide production during forward electron transport.

Flavoprotein autofluorescence imaging in the cerebellar cortex in vivo

Autofluorescence optical imaging is rapidly becoming a widely used tool for mapping activity in the central nervous system function in vivo and investigating the coupling among neurons, glia, and metabolism. This paper provides a brief review of autofluorescence and of our recent work using flavoprotein imaging in the cerebellar cortex. Stimulation of the parallel fibers evokes an intrinsic fluorescence signal that is tightly coupled to neuronal activation and primarily generated postsynaptically. The signal originates from mitochondrial flavoproteins. The signal is biphasic, with the initial increase in fluorescence (light phase) resulting from the oxidation of flavoproteins and the subsequent decrease (dark phase) from the reduction of flavoproteins. The light phase is primarily neuronal, and the dark phase is primarily glial. Exploiting the spatial properties of molecular layer inhibition in the cerebellar cortex, we show that flavoprotein autofluorescence can monitor both excitatory and inhibitory activity in the cerebellar cortex. Furthermore, flavoprotein autofluorescence has revealed that molecular layer inhibition is organized into parasagittal domains that differentially modulate the spatial pattern of cerebellar cortical activity. The reduction in flavoprotein autofluorescence occurring in the inhibitory bands most likely reflects a decrease in intracellular Ca(2+) in the neurons inhibited by the molecular layer interneurons. Therefore, flavoprotein autofluorescence imaging is providing new insights into cerebellar cortical function and neurometabolic coupling.

Intracellular free iron and acidic pathways mediate TNF-induced death of rat hepatoma cells

Rat hepatoma HTC cells are intrinsically resistant to various apoptosis-inducing agents. Strategies to induce death in hepatoma cells are needed and the present experimental study was aimed to investigate the sensitivity of HTC cells to TNF and to clarify the mechanisms of action of this cytokine. Cells were treated with TNF and death mechanisms characterized employing an integration of morphological and biochemical techniques. HTC cells, sensitized to TNF toxicity with cycloheximide, died in a caspase-independent apoptosis-like manner. Although we found no evidence for a direct involvement of lysosomal cathepsins, bafilomycin A1 and ammonium chloride significantly attenuated TNF toxicity. Also desferrioxamine mesylate, an iron chelator, partly protected the cells from TNF, while a complete protection was afforded by combining ammonium chloride and iron chelator. Moreover, HTC were protected from TNF also by lipophylic antioxidants and diphenylene iodonium chloride, a NADPH oxidase inhibitor. These data depict a novel mechanism of TNF-mediated cytotoxicity in HTC cells, in which the endo-lysosomal compartment, NADPH oxidase and an iron-mediated pro-oxidant status contribute in determining a caspase-independent, apoptosis-like cell death.

NADH as Donor

The number of NADH dehydrogenases and their role in energy transduction in Escherchia coli have been under debate for a long time. Now it is evident that E. coli possesses two respiratory NADH dehydrogenases, or NADH:ubiquinone oxidoreductases, that have traditionally been called NDH-I and NDH-II. This review describes the properties of these two NADH dehydrogenases, focusing on the mechanism of the energy converting NADH dehydrogenase as derived from the high resolution structure of the soluble part of the enzyme. In E. coli , complex I operates in aerobic and anaerobic respiration, while NDH-II is repressed under anaerobic growth conditions. The insufficient recycling of NADH most likely resulted in excess NADH inhibiting tricarboxylic acid cycle enzymes and the glyoxylate shunt. Salmonella enterica serovar Typhimurium complex I mutants are unable to activate ATP-dependent proteolysis under starvation conditions. NDH-II is a single subunit enzyme with a molecular mass of 47 kDa facing the cytosol. Despite the absence of any predicted transmembrane segment it has to be purified in the presence of detergents, and the activity of the preparation is stimulated by an addition of lipids.

The ND1 Subunit Constructs the Inhibitor Binding Domain in Bovine Heart Mitochondrial Complex I

The inhibitor binding domain in bovine complex I is believed to be constructed by multisubunits, but it remains to be learned how the binding positions of chemically diverse inhibitors relate to each other. To get insight into the inhibitor binding domain in complex I, we synthesized a photoreactive acetogenin [[125I](trifluoromethyl)phenyldiazirinylacetogenin, [125I]TDA], in which an aryldiazirine group serves as both a photoreactive group and a substitute for the gamma-lactone ring that is a common toxophore of numerous natural acetogenins, and carried out photoaffinity labeling to identify the labeled subunit using bovine heart submitochondrial particles (SMP). When SMP were UV-irradiated in the presence of [125I]TDA, radioactivity was predominantly incorporated into an approximately 30 kDa band on a SDS gel. Blue native gel electrophoresis of the [125I]TDA-labeled SMP revealed that the majority of radioactivity was observed in complex I. Analysis of complex I on a SDS gel showed a predominant peak of radioactivity at approximately 30 kDa. Immnoprecipitation of the [125I]TDA-labeled complex I with anti-bovine ND1 antibody indicated that the labeled protein is the ND1 subunit. A variety of complex I inhibitors such as piericidin A and rotenone efficiently suppressed the specific binding of [125I]TDA to ND1, indicating that they share a common binding domain. However, the suppression efficiency of Deltalac-acetogenin, a new type of complex I inhibitor synthesized in our laboratory, was much lower than that of the traditional inhibitors. Our results unequivocally reveal that the ND1 subunit constructs the inhibitor binding domain, though the contribution of this subunit has been challenged. Further, the present study corroborates our previous proposition that the inhibition site of Deltalac-acetogenins differs from that of traditional inhibitors.

Mode of Inhibitory Action of Δlac-Acetogenins, a New Class of Inhibitors of Bovine Heart Mitochondrial Complex I

We have revealed that Deltalac-acetogenins, a new class of inhibitors of bovine heart mitochondrial complex I (NADH-ubiquinone oxidoreductase), act differently from ordinary inhibitors such as rotenone and piericidin A [Ichimaru et al. (2005) Biochemistry 44, 816-825]. Since a detailed study of these unique inhibitors might provide new insight into the terminal electron transfer step of the enzyme, we further characterized their inhibitory action using the most potent Deltalac-acetogenin derivative (compound 1). Unlike ordinary complex I inhibitors, 1 had a dose-response curve for inhibition of the reduction of exogenous short-chain ubiquinones that was difficult to explain with a simple bimolecular association model. The inhibitory effect of 1 on ubiquinol-NAD(+) oxidoreductase activity (reverse electron transfer) was much weaker than that on NADH oxidase activity (forward electron transfer), indicating a direction-specific effect. These results suggest that the binding site of 1 is not identical to that of ubiquinone and the binding of 1 to the enzyme secondarily (or indirectly) disturbs the redox reaction of ubiquinone. Using endogenous and exogenous ubiquinone as an electron acceptor of complex I, we investigated the effect of 1 in combination with different ordinary inhibitors on the superoxide production from the enzyme. The results indicated that the level of superoxide production induced by 1 is significantly lower than that induced by ordinary inhibitors probably because of fewer electron leaks from the ubisemiquinone radical to molecular oxygen and that the site of inhibition by 1 is downstream of that by ordinary inhibitors. The unique inhibitory action of hydrophobic Deltalac-acetogenins may be closely associated with the dynamic function of the membrane domain of complex I.

Energy converting NADH:quinone oxidoreductase (complex I)

NADH:quinone oxidoreductase (complex I) pumps protons across the inner membrane of mitochondria or the plasma membrane of many bacteria. Human complex I is involved in numerous pathological conditions and degenerative processes. With 14 central and up to 32 accessory subunits, complex I is among the largest membrane-bound protein assemblies. The peripheral arm of the L-shaped molecule contains flavine mononucleotide and eight or nine iron-sulfur clusters as redox prosthetic groups. Seven of the iron-sulfur clusters form a linear electron transfer chain between flavine and quinone. In most organisms, the seven most hydrophobic subunits forming the core of the membrane arm are encoded by the mitochondrial genome. Most central subunits have evolved from subunits of different hydrogenases and bacterial Na+/H+ antiporters. This evolutionary origin is reflected in three functional modules of complex I. The coupling mechanism of complex I most likely involves semiquinone intermediates that drive proton pumping through redox-linked conformational changes.

Mitochondrial Complex I: structural and functional aspects

This review examines two aspects of the structure and function of mitochondrial Complex I (NADH Coenzyme Q oxidoreductase) that have become matter of recent debate. The supramolecular organization of Complex I and its structural relation with the remainder of the respiratory chain are uncertain. Although the random diffusion model [C.R. Hackenbrock, B. Chazotte, S.S. Gupte, The random collision model and a critical assessment of diffusion and collision in mitochondrial electron transport, J. Bioenerg. Biomembranes 18 (1986) 331-368] has been widely accepted, recent evidence suggests the presence of supramolecular aggregates. In particular, evidence for a Complex I-Complex III supercomplex stems from both structural and kinetic studies. Electron transfer in the supercomplex may occur by electron channelling through bound Coenzyme Q in equilibrium with the pool in the membrane lipids. The amount and nature of the lipids modify the aggregation state and there is evidence that lipid peroxidation induces supercomplex disaggregation. Another important aspect in Complex I is its capacity to reduce oxygen with formation of superoxide anion. The site of escape of the single electron is debated and either FMN, iron-sulphur clusters, and ubisemiquinone have been suggested. The finding in our laboratory that two classes of hydrophobic inhibitors have opposite effects on superoxide production favours an iron-sulphur cluster (presumably N2) is the direct oxygen reductant. The implications in human pathology of better knowledge on these aspects of Complex I structure and function are briefly discussed.

Estrogen-induced DNA synthesis in vascular endothelial cells is mediated by ROS signaling

Background

Since estrogen is known to increase vascular endothelial cell growth, elevated estrogen exposure from hormone replacement therapy or oral contraceptives has the potential to contribute in the development of abnormal proliferative vascular lesions and subsequent thickening of the vasculature. How estrogen may support or promote vascular lesions is not clear. We have examined in this study whether estrogen exposure to vascular endothelial cells increase the formation of reactive oxygen species (ROS), and estrogen-induced ROS is involved in the growth of endothelial cells.

Methods

The effect of estrogen on the production of intracellular oxidants and the role of estrogen-induced ROS on cell growth was studied in human umbilical vein endothelial cells. ROS were measured by monitoring the oxidation of 2'7'-dichlorofluorescin by spectrofluorometry. Endothelial cell growth was measured by a colorimetric immunoassay based on BrdU incorporation into DNA.

Results

Physiological concentrations of estrogen (367 fmol and 3.67 pmol) triggered a rapid 2-fold increase in intracellular oxidants in endothelial cells. E2-induced ROS formation was inhibited to basal levels by cotreatment with the mitochondrial inhibitor rotenone (2 μM) and xanthine oxidase inhibitor allopurinol (50 μM). Inhibitors of NAD(P)H oxidase, apocynin and DPI, did not block E2-induced ROS formation. Furthermore, the NOS inhibitor, L-NAME, did not prevent the increase in E2-induced ROS. These findings indicate both mitochondria and xanthine oxidase are the source of ROS in estrogen treated vascular endothelial cells. E2 treated cells showed a 2-fold induction of BrdU incorporation at 18 h which was not observed in cells exposed to vehicle alone. Cotreatment with ebselen (20 μM) and NAC (1 mM) inhibited E2-induced BrdU incorporation without affecting the basal levels of DNA synthesis. The observed inhibitory effect of NAC and ebselen on E2-induced DNA synthesis was also shown to be dose dependent.

Conclusion

We have shown that estrogen exposure stimulates the rapid production of intracellular ROS and they are involved in growth signaling of endothelial cells. It appears that the early estrogen signaling does not require estrogen receptor genomic signaling because we can inhibit estrogen-induced DNA synthesis by antioxidants. Findings of this study may further expand research defining the underlying mechanism of how estrogen may promote vascular lesions. It also provides important information for the design of new antioxidant-based drugs or new antioxidant gene therapy to protect the cardiovascular health of individuals sensitive to estrogen.

Respiratory burst and NAD(P)H oxidase activity are involved in capacitation of cryopreserved bovine spermatozoa

Heparin (a glycosaminoglycan) and quercetin (a calcium-ATPase plasma membrane specific inhibitor) induce bovine sperm capacitation. Mitochondria from frozen semen are capable of generating oxidative energy. The aim of the study was to determine oxygen uptake variation and the participation of diphenileneiodonium (DPI)-sensitive oxidases from spermatozoa capacitated with heparin or quercetin. Oxygen uptake was measured polarographically and 2 microM diphenileneiodonium (DPI) was used as a specific inhibitor of NAD(P)H-oxidases. Sperm capacitation was determined by the chlorotetracycline technique. Heparin produced a respiratory burst (17.0+/-3.2 microL O2/h/10(8) spermatozoa; mean+/-S.D.) versus control (11.3+/-0.9 microL O2/h/10(8) spermatozoa; P<0.05). Oxygen uptake and sperm hypermotility were inhibited by cyanide. Treatment with DPI blocked heparin capacitation and oxygen uptake (cyanide-sensitive) decreased to control levels. Respiration of quercetin-treated samples (cyanide-sensitive; 9.7+/-0.7 microL O2/h/10(8) spermatozoa) was not significantly different from the controls; oxygen uptake was not modified by DPI, but quercetin capacitation was inhibited (P<0.05). The effect of DPI with heparin confirmed that oxidases participate in capacitation induction. The addition of superoxide dismutase and/or catalase to heparin- or quercetin-treated samples, failed to modify oxygen uptake and blocked capacitation (P<0.05), suggesting that the superoxide anion (O2*-) participates in the capacitation induction. High mitochondrial activity from heparin-treated samples indicated that energy requirements, especially for hypermotility, were supported by the respiratory chain. Although a respiratory burst was not produced by quercetin, DPI-sensitive-oxidases (O2*- source) were necessary for capacitation. In cryopreserved bovine spermatozoa, heparin- or quercetin-induced capacitation required different levels of mitochondrial energy and DPI-sensitive oxidase activity.

Actions of a histone deacetylase inhibitor NSC3852 (5-nitroso-8-quinolinol) link reactive oxygen species to cell differentiation and apoptosis in MCF-7 human mammary tumor cells

NSC3852 (5-nitroso-8-quinolinol) has cell differentiation and antiproliferative activity in human breast cancer cells in tissue culture and antitumor activity in mice bearing P388 and L1210 leukemic cells. We investigated the mechanism of NSC3852 action in MCF-7 human breast cancer cells using electron spin resonance (ESR). Reactive oxygen species (ROS) were detected in MCF-7 cell suspensions incubated with NSC3852 using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Formation of the DMPO-OH adduct was quenched by the addition of superoxide dismutase but not by catalase, and we concluded that superoxide was generated in the NSC3852-treated cells. The flavoprotein inhibitor diphenylene iodonium suppressed ROS production, providing evidence for the involvement of a flavin-dependent enzyme system in the ROS response to NSC3852. A biologically significant oxidative response to NSC3852 occurred in MCF-7 cells. An early marker of oxidative stress was a decrease in the [glutathione]/[glutathione disulfide] ratio 1 h after NSC3852 addition. Oxidative DNA damage, marked by the presence of 8-oxoguanine, and DNA-strand breakage occurred in cells exposed to NSC3852 for 24 h. Apoptosis peaked 48 h after exposure to NSC3852. Pretreatment with the glutathione precursor N-acetyl-l-cysteine (NAC) prevented DNA-strand breakage and apoptosis. Pretreatment with NAC also reversed NSC3852 decreases in E2F1, Myc, and phosphorylated retinoblastoma protein, indicative of redox-sensitive pathway(s) in MCF-7 cells during G(1) phase of the cell cycle. We conclude that ROS formation is involved in the apoptotic and cell differentiation responses to NSC3852 in MCF-7 cells.

EGFR kinase regulates volume-sensitive chloride current elicited by integrin stretch via PI-3K and NADPH oxidase in ventricular myocytes

Stretch of beta1 integrins activates an outwardly rectifying, tamoxifen-sensitive Cl(-) current (Cl(-) SAC) via AT1 receptors, NADPH oxidase, and reactive oxygen species, and Cl(-) SAC resembles the volume-sensitive Cl(-) current (I(Cl,swell)). Epidermal growth factor receptor (EGFR) kinase undergoes transactivation upon stretch, integrin engagement, and AT1 receptor activation and, in turn, stimulates NADPH oxidase. Therefore, we tested whether Cl(-) SAC is regulated by EGFR kinase signaling and is volume sensitive. Paramagnetic beads coated with mAb for beta1 integrin were attached to myocytes and pulled with an electromagnet. Stretch activated a Cl(-) SAC that was 1.13 +/- 0.10 pA/pF at +40 mV. AG1478 (10 muM), an EGFR kinase blocker, inhibited 93 +/- 13% of Cl(-) SAC, and intracellular pretreatment with 1 muM AG1478 markedly suppressed Cl(-) SAC activation. EGF (3.3 nM) directly activated an outwardly rectifying Cl(-) current (0.81 +/- 0.05 pA/pF at +40 mV) that was fully blocked by 10 muM tamoxifen, an I(Cl,swell) blocker. Phosphatidylinositol 3-kinase (PI-3K) is downstream of EGFR kinase. Wortmannin (500 nM) and LY294002 (100 microM), blockers of PI-3K, inhibited Cl(-) SAC by 67 +/- 6% and 91 +/- 25% respectively, and the EGF-induced Cl(-) current also was fully blocked by LY294002. Furthermore, gp91ds-tat (500 nM), a cell-permeable, chimeric peptide that specifically blocks NADPH oxidase assembly, profoundly inhibited the EGF-induced Cl(-) current. Inactive permeant and active impermeant control peptides had no effect. Myocyte shrinkage with hyperosmotic bathing media inhibited the Cl(-) SAC and EGF-induced Cl(-) current by 88 +/- 9% and 127 +/- 11%, respectively. These results suggest that beta1 integrin stretch activates Cl(-) SAC via EGFR, PI-3K, and NADPH oxidase, and that both the Cl(-) SAC and the EGF-induced Cl(-) currents are likely to be the volume-sensitive Cl(-) current, I(Cl,swell).

Heat shock-induced attenuation of hydroxyl radical generation and mitochondrial aconitase activity in cardiac H9c2 cells

A mild heat shock (hyperthermia) protects cells from apoptotic and necrotic deaths by inducing overexpression of various heat shock proteins (Hsps). These proteins, in combination with the activation of the nitric oxide synthase (NOS) enzyme, play important roles in the protection of the myocardium against a variety of diseases. In the present work we report that the generation of potent reactive oxygen species (ROS), namely ·OH in cardiac H9c2 cells, is attenuated by heat shock treatment (2 h at 42°C). Western blot analyses showed that heat shock treatment induced overexpression of Hsp70, Hsp60, and Hsp25. The observed ·OH was found to be derived from the superoxide (O2−·) generated by the mitochondria. Whereas the manganese superoxide dismutase (MnSOD) activity was increased in the heat-shocked cells, the mitochondrial aconitase activity was reduced. The mechanism of O2−· conversion into ·OH in mitochondria is proposed as follows. The O2−· leaked from the electron transport chain, oxidatively damages the mitochondrial aconitase, releasing a free Fe2+. The aconitase-released Fe2+combines with H2O2to generate ·OH via a Fenton reaction and the oxidized Fe3+recombines with the inactivated enzyme after being reduced to Fe2+by other cellular reductants, turning it over to be active. However, in heat-shocked cells, because of higher MnSOD activity, the excess H2O2causes irreversible damage to the mitochondrial aconitase enzyme, thus inhibiting its activity. In conclusion, we propose that attenuation of ·OH generation after heat shock treatment might play an important role in reducing the myocardial ischemic injury, observed in heat shock-treated animals.

Pyrroloquinoline quinone modulates mitochondrial quantity and function in mice

When pyrroloquinoline quinone (PQQ) is added to an amino acid-based, but otherwise nutritionally complete basal diet, it improves growth-related variables in young mice. We examined PQQ and mitochondrial function based on observations that PQQ deficiency results in elevated plasma glucose concentrations in young mice, and PQQ addition stimulates mitochondrial complex 1 activity in vitro. PQQ-deficient weanling mice had a 20-30% reduction in the relative amount of mitochondria in liver; lower respiratory control ratios, and lower respiratory quotients than PQQ-supplemented mice (2 mg PQQ/kg diet). In mice from dams fed a conventional laboratory diet, but switched at weaning to the basal diet, plasma glucose, Ala, Gly, and Ser concentrations were elevated at 4 wk (PQQ- vs. PQQ+), but not at 8 wk. The relative mitochondrial content (ratio of mtDNA to nuclear DNA) also tended (P<0.18) to be lower (PQQ- vs. PQQ+) at 4 wk, but not at 8 wk. PQQ also counters the mitochondrial complex 1 inhibitor, diphenylene iodonium (DPI). Mice were gavaged with 0, 0.4, or 4 microg PQQ/g body weight (BW) daily for 14 d. At each PQQ level, DPI was injected (i.p.) at 0, 0.4, 0.8, or 1.6 microg DPI/g BW. The PQQ-deficient mice exposed to 0.4 or 4.0 microg DPI/g lost weight and had lower plasma glucose levels than PQQ-supplemented mice (P<0.05). In addition, fibroblasts took up (3)H-PQQ added to cell cultures, and cultured hepatocytes maintained mitochondrial PQQ concentrations similar to those observed in vivo. Collectively, these results indicate that dietary PQQ can influence mitochondrial amount and function, particularly in perinatal and weanling mice.

Hepatitis C virus core protein: an update on its molecular biology, cellular functions and clinical implications

The present review article is an update on various features of hepatitis C virus (HCV) core protein including its molecular biology, role in HCV replication, involvement in HCV pathogenesis, etiological role in hepatocellular carcinogenesis, significance in diagnosis and vaccination against HCV infection. Core protein is a structural protein of HCV virus and has only recently been characterized. It was found to play a major role in HCV-induced viral hepatitis. Although published information shows a lot about the clinical significance of HCV core protein, several studies are still needed to demonstrate its exact significance in viral biology and underlying HCV pathogenesis.

Hyperoxia-induced reactive oxygen species formation in pulmonary capillary endothelial cells in situ

Lung capillary endothelial cells (ECs) are a critical target of oxygen toxicity and play a central role in the pathogenesis of hyperoxic lung injury. To determine mechanisms and time course of EC activation in normobaric hyperoxia, we measured endothelial concentration of reactive oxygen species (ROS) and cytosolic calcium ([Ca(2+)](i)) by in situ imaging of 2',7'-dichlorofluorescein (DCF) and fura 2 fluorescence, respectively, and translocation of the small GTPase Rac1 by immunofluorescence in isolated perfused rat lungs. Endothelial DCF fluorescence and [Ca(2+)](i) increased continuously yet reversibly during a 90-min interval of hyperoxic ventilation with 70% O(2), demonstrating progressive ROS generation and second messenger signaling. ROS formation increased exponentially with higher O(2) concentrations. ROS and [Ca(2+)](i) responses were blocked by the mitochondrial complex I inhibitor rotenone, whereas inhibitors of NAD(P)H oxidase and the intracellular Ca(2+) chelator BAPTA predominantly attenuated the late phase of the hyperoxia-induced DCF fluorescence increase after > 30 min. Rac1 translocation in lung capillary ECs was barely detectable at normoxia but was prominent after 60 min of hyperoxia and could be blocked by rotenone and BAPTA. We conclude that hyperoxia induces ROS formation in lung capillary ECs, which initially originates from the mitochondrial electron transport chain but subsequently involves activation of NAD(P)H oxidase by endothelial [Ca(2+)](i) signaling and Rac1 activation. Our findings demonstrate rapid activation of ECs by hyperoxia in situ and identify mechanisms that may be relevant in the initiation of hyperoxic lung injury.

Inhibitor studies on non-photochemical plastoquinone reduction and H(2) photoproduction in Chlamydomonas reinhardtii

In the absence of PSII, non-photochemical reduction of plastoquinones (PQs) occurs following NADH or NADPH addition in thylakoid membranes of the green alga Chlamydomonas reinhardtii. The nature of the enzyme involved in this reaction has been investigated in vitro by measuring chlorophyll fluorescence increase in anoxia and light-dependent O(2) uptake in the presence of methyl viologen. Based on the insensitivity of these reactions to rotenone, a type-I NADH dehydrogenase (NDH-1) inhibitor, and their sensitivity to flavoenzyme inhibitors and thiol blocking agents, we conclude to the involvement of a type-II NADH dehydrogenase (NDH-2) in PQ reduction. Intact Chlamydomonas cells placed in anoxia have the property to produce H(2) in the light by a Fe-hydrogenase which uses reduced ferredoxin as an electron donor. H(2) production also occurs in the absence of PSII thanks to the existence of a non-photochemical pathway of PQ reduction. From inhibitors effects, we suggest the involvement of a plastidial NDH-2 in PSII-independent H(2) production in Chlamydomonas. These results are discussed in relation to the absence of ndh genes in Chlamydomonas plastid genome and to the existence of 7 ORFs homologous to type-II NDHs in its nuclear genome.

Superoxide Radical Formation by Pure Complex I (NADH:Ubiquinone Oxidoreductase) from Yarrowia lipolytica

Generation of reactive oxygen species (ROS) is increasingly recognized as an important cellular process involved in numerous physiological and pathophysiological processes. Complex I (NADH:ubiquinone oxidoreductase) is considered as one of the major sources of ROS within mitochondria. Yet, the exact site and mechanism of superoxide production by this large membrane-bound multiprotein complex has remained controversial. Here we show that isolated complex I from Yarrowia lipolytica forms superoxide at a rate of 0.15% of the rate measured for catalytic turnover. Superoxide production is not inhibited by ubiquinone analogous inhibitors. Because mutant complex I lacking a detectable iron-sulfur cluster N2 exhibited the same rate of ROS production, this terminal redox center could be excluded as a source of electrons. From the effect of different ubiquinone derivatives and pH on this side reaction of complex I we concluded that oxygen accepts electrons from FMNH2 or FMN semiquinone either directly or via more hydrophilic ubiquinone derivatives.

Involvement of the pentose phosphate pathway and redox regulation in fertilization in the mouse

Glucose metabolism is necessary for successful fertilization in the mouse. Both spermatozoa and oocytes metabolize glucose through the pentose phosphate pathway (PPP), and NADPH appears required for gamete fusion. The aims of this study were to further characterize the utilization of glucose by the fertilizing spermatozoon and the fertilized oocyte, to demonstrate the importance of the PPP in different steps of fertilization, and to examine whether the beneficial effect of glucose could be mediated by a NADPH-dependent enzyme involved in redox regulation. By using a fluorescent analog of 2-deoxyglucose, glucose uptake was evidenced in both the head and flagellum of motile spermatozoa. After sperm-oocyte fusion, an increase in glucose uptake by the fertilized oocyte was observed but not before the formation of the male and female pronuclei. By using a microphotometric technique, activity of glucose 6-phosphate dehydrogenase (G6PDH), the key enzyme of the PPP, was localized to the sperm head and midpiece. When epididymal spermatozoa were released into a glucose-containing medium, the NADPH/NADP ratio increased with capacitation. Sperm-oocyte fusion and meiosis reinitiation of the fertilized oocyte was inhibited by the PPP inhibitor 6-aminonicotinamide (6-AN); inhibition of sperm-oocyte fusion was relieved by NADPH. Sperm-oocyte fusion and meiosis reinitiation were also inhibited by diphenylamine iodonium, which is a flavoenzyme inhibitor reported to prevent reactive oxygen species (ROS) generation in mouse spermatozoa and embryos. These findings indicate that the PPP is involved in different steps of fertilization. Subsequent regulation of a NADPH-dependent flavoenzyme responsible of ROS production is envisaged.

Cytochrome P4502E1 primes macrophages to increase TNF-alpha production in response to lipopolysaccharide

Kupffer cells become activated in response to elevated levels of LPS during ethanol feeding, but the role of ethanol in the molecular processes of activation remains unclear. Because cytochrome P4502E1 (CYP2E1) is upregulated in Kupffer cells after ethanol, we hypothesized that this effect primes Kupffer cells, sensitizing them to increase TNF-alpha production in response to LPS. However, cultured Kupffer cells rapidly lose their CYP2E1. This difficulty was overcome by transfecting CYP2E1 to RAW 264.7 macrophages. Macrophages with stable increased CYP2E1 expression (E2) displayed increased levels of CD14/Toll-like receptor 4, NADPH oxidase and H2O2, accompanied by activation of ERK1/2, p38, and NF-kappaB. These increases primed E2 cells, sensitizing them to LPS stimuli, with amplification of LPS signaling, resulting in increased TNF-alpha production. Diphenyleneiodonium, a NADPH oxidase inhibitor, and diallyl sulfide, a CYP2E1 inhibitor, decreased approximately equally H2O2 levels in E2 cells, suggesting that NADPH oxidase and CYP2E1 contribute equally to H2O2 generation. Because CYP2E1 expression also enhanced the levels of the membrane localized NADPH oxidase subunits p47phox and p67phox, thereby contributing to the oxidase activation, it may augment H2O2 generation via this mechanism. H2O2, derived in part from NADPH and CYP2E1, activated ERK1/2 and p38. ERK1/2 stimulated TNF-alpha production via activation of NF-kappaB, whereas p38 promoted TNF-alpha production by stabilizing TNF-alpha mRNA. Oxidant generation after CYP2E1 overexpression appears to be central to macrophage priming and their sensitization to LPS. Accordingly, CYP2E1 priming could explain the sensitization of Kupffer cells to LPS activation by ethanol, a critical early step in alcoholic liver disease.

Hypoxic pulmonary vasoconstriction: redox events in oxygen sensing

Recently, the mitochondria have become the focus of attention as the site of O(2) sensing underlying hypoxic pulmonary vasoconstriction (HPV). However, two disparate models have emerged to explain how mitochondria react to a decrease in Po(2). One model proposes that a drop in Po(2) decreases the rate of mitochondrial reactive oxygen species (ROS) generation, resulting in a decrease in oxidant stress and an accumulation of reducing equivalents. The resulting shift of the cytosol to a reduced state causes the inhibition of voltage-dependent potassium channels, membrane depolarization, and the influx of calcium through voltage-gated (L-type) calcium channels. A second and opposing model suggests that hypoxia triggers a paradoxical increase in a mitochondrial-induced ROS signal. The resulting shift of the cytosol to an oxidized state triggers the release of intracellular calcium stores, recruitment of calcium channels in the plasma membrane, and activation of contraction. This article summarizes the potential involvement of a mitochondria-induced ROS signal in these two very different models.

Increased superoxide anion in rostral ventrolateral medulla contributes to hypertension in spontaneously hypertensive rats via interactions with nitric oxide

Oxidative stress because of an excessive production of superoxide anion (O2*-) is associated with hypertension. The present study evaluated the hypothesis that in the rostral ventrolateral medulla (RVLM), where the premotor neurons for the maintenance of vascular vasomotor activity are located, increased O2*- contributes to hypertension in spontaneously hypertensive rats (SHR) by modulating the cardiovascular depressive actions of nitric oxide (NO). Compared with normotensive Wistar-Kyoto (WKY) rats, SHR manifested significantly increased basal O2*- production, along with reduced manganese superoxide dismutase (MnSOD) expression and activity, in the RVLM. The magnitude of hypotension, bradycardia, or suppression of sympathetic neurogenic vasomotor tone elicited by microinjection bilaterally into the RVLM of a membrane-permeable SOD mimetic, Mn(III)-tetrakis-(4-benzoic acid) porphyrin (MnTBAP), was also significantly larger in SHR. Transfection bilaterally into the RVLM of adenoviral vectors encoding endothelial nitric oxide synthase resulted in suppression of arterial pressure, heart rate, and sympathetic neurogenic vasomotor tone in both WKY rats and SHR. Microinjection of MnTBAP into the RVLM of SHR further normalized those cardiovascular parameters to the levels of WKY rats. We conclude that an elevated level of O2*- in the RVLM is associated with hypertension in SHR. More importantly, this elevated O2*- may contribute to hypertension by reducing the NO-promoted cardiovascular depression.

Synthesis and Inhibition Mechanism of Δlac-Acetogenins, a Novel Type of Inhibitor of Bovine Heart Mitochondrial Complex I

We have synthesized Deltalac-acetogenins that are new acetogenin mimics possessing two n-alkyl tails without an alpha,beta-unsaturated gamma-lactone ring and suggested that their inhibition mechanism may be different from that of common acetogenins [Hamada et al. (2004) Biochemistry 43, 3651-3658]. To elucidate the inhibition mechanism of Deltalac-acetogenins in more detail, we carried out wide structural modifications of original Deltalac-acetogenins and characterized the inhibitory action with bovine heart mitochondrial complex I. In contrast to common acetogenins, both the presence of adjacent bis-THF rings and the stereochemistry around the hydroxylated bis-THF rings are important structural factors required for potent inhibition. The inhibitory potency of a derivative possessing an n-butylphenyl ether structure (compound 7) appeared to be superior to that of the original Deltalac-acetogenins and equivalent to that of bullatacin, one of the most potent natural acetogenins. Double-inhibitor titration of steady-state complex I activity showed that the extent of inhibition of compound 7 and bullatacin is not additive, suggesting that the binding sites of the two inhibitors are not identical. Competition tests using a fluorescent ligand indicated that the binding site of compound 7 does not overlap with that of other complex I inhibitors. The effects of compound 7 on superoxide production from complex I are also different from those of other complex I inhibitors. Our results clearly demonstrate that Deltalac-acetogenins are a novel type of inhibitor acting at the terminal electron-transfer step of bovine complex I.

Preconditioning by isoflurane is mediated by reactive oxygen species generated from mitochondrial electron transport chain complex III

Reactive oxygen species (ROS) mediate volatile anesthetic preconditioning. We tested the hypothesis that isoflurane (ISO) generates ROS from electron transport chain complexes I and III. Rabbits (n = 55) underwent 30 min coronary artery occlusion followed by 3 h reperfusion and received 0.9% saline, the complex I inhibitor diphenyleneiodonium (DPI; 1.5 mg/kg bolus followed by 1.5 mg/kg over 1 h), or the complex III inhibitor myxothiazol (MYX; 0.1 mg/kg bolus followed by 0.3 mg/kg over 1 h) in the absence and presence of 1.0 minimum alveolar concentration ISO. ISO was administered for 30 min and discontinued 15 min before coronary occlusion. Infarct size and ROS production (n = 32) were determined using triphenyltetrazolium staining and ethidium-DNA fluorescence, respectively. Adenosine triphosphate (ATP) synthesis in mitochondria obtained from rabbit hearts (n = 24) subjected to drug interventions was measured by luciferin-luciferase luminometry. ISO significantly (P < 0.05) reduced infarct size (19% +/- 4%) as compared with control (39% +/- 4%). MYX (35% +/- 4%), but not DPI (24% +/- 2%), abolished this protection. ISO increased ethidium-DNA fluorescence (83 +/- 11 U) as compared with control (40 +/- 12 U). MYX (35 +/- 3 U), but not DPI (78 +/- 9 U), abolished ROS generation. DPI and MYX selectively reduced complex I- and complex III-mediated ATP synthesis, respectively. ROS generated from electron transport chain complex III mediate ISO-induced cardioprotection.

Rodent and human mast cells produce functionally significant intracellular reactive oxygen species but not nitric oxide

In immunity, reactive oxygen species (ROS) and nitric oxide (NO) are important antimicrobial agents and regulators of cell signaling and activation pathways. However, the cellular sources of ROS and NO are much debated. Particularly, there is contention over whether mast cells, key secretory cells in allergy and immunity, can generate these chemical species, and if so, whether they are of functional significance. We therefore examined directly by flow cytometry the capacity of mast cells to generate intracellular ROS and NO using the respective cell-permeable fluorescent probes dichlorodihydrofluorescein and diaminofluorescein and evaluated the effects of inhibitors of ROS and NO synthesis on cell degranulation. For each of three mast cell types (rat peritoneal mast cells, mouse bone marrow-derived mast cells, and human blood-derived mast cells), degranulation stimulated by IgE/antigen was accompanied by production of intracellular ROS but not NO. Inhibition of ROS production led to reduced degranulation, indicating a facilitatory role for ROS, whereas NO synthase inhibitors were without effect. Likewise, bacterial lipopolysaccharide and interferon-gamma over a wide range of conditions failed to generate intracellular NO in mast cells, whereas these agents readily induced intracellular NO in macrophages. NO synthase protein, as assessed by Western blotting, was readily induced in macrophages but not mast cells. We conclude that rodent and human mast cells generate intracellular ROS but not NO and that intracellular ROS but not intracellular NO are functionally linked to mast cell degranulation.