Diphenylene iodonium as an inhibitor of the NADPH oxidase complex of bovine neutrophils. Factors controlling the inhibitory potency of diphenylene iodonium in a cell-free system of oxidase activation

Diphenyleneiodonium and dimethylsulfoxide for treatment of reperfusion injury in cerebral ischemia of the rat

Diphenyleneiodonium (DPI) is an inhibitor of the free radical producing NAD(P)H-oxidase. We tested whether DPI shows neuroprotective properties after focal cerebral ischemia and we used dimethylsulfoxide (DMSO), a nonspecific free radical scavenger, as a solvent. In male Wistar rats middle cerebral artery occlusion (1.5 h) and subsequent reperfusion (48 h) (MCAO/R) was induced with the filament model. Immediately after reperfusion the animals received either 0.25 ml normal saline, DMSO, or a combination of DMSO and DPI; each group consisted of 10 animals. MRI was performed at different times after reperfusion. Gelatine zymography of brain tissue for MMP-2 and MMP-9 was performed. The infarct sizes and BBB damage showed a significant difference between controls and the DPI/DMSO group for almost all points in time in all sequences. The activity of MMP-2 and MMP-9 was significantly reduced by DPI/DMSO but not by DMSO alone. DMSO treatment alone resulted in a protective effect with reduced lesion sizes measured by MRI at selected points of time, consistent with its known free radical scavenger effect. The combination of DMSO with DPI partly augmented this effect, presumably due to the additional inhibition of MMP-2 and MMP-9 by DPI. Moreover, the neurological outcome in both therapeutic groups was improved compared to controls with a significant difference between the therapeutic groups in favour of DPI and DMSO. The combination of DPI and DMSO reduced the activity of MMP-2 and MMP-9, attenuated the postischemic blood-brain barrier damage and improved neurological outcome. This was most likely due to reduced oxidative stress.

The enhanced monocyte adhesiveness after UVB exposure requires ROS and NF-kappaB signaling in human keratinocyte

The infiltration of both monocyte and activated T cells in the skin is one of critical steps in the development of UVB-induced inflammation. Upregulation of adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1) on the surface of keratinocytes plays an important role in this process. In this study, we examined the molecular mechanism responsible for UVB-induced expression of ICAM-1 and subsequent monocyte adhesion by keratinocyte. We observed that (1) UVB induced protein and mRNA expression of ICAM-1 in a dose- and time-dependent manner in human keratinocyte cell HaCaT; (2) UVB induced the translocation of NF-kappaB and inhibition of NF-kappaB by NF-kappaB inhibitors suppressed UVB-induced mRNA and protein expression of ICAM-1; (3) UVB increased the intracellular level of reactive oxygen species (ROS) by HaCaT cells; (4) UVB-induced increase of intracellular ROS level was suppressed by pretreatment with diphenyl iodonium (DPI) and N-acetyl cysteine (NAC); and (5) inhibition of UVB-induced ROS production by DPI or NAC suppressed UVB-mediated translocation of NF-kappaB, expression of ICAM-1 and subsequent monocyte adhesion in HaCaT cells. These results suggest that UVB-induced ROS is involved in the translocation of NF-kappaB which is responsible for expression of ICAM-1 and subsequent increased monocyte adhesion in human keratinocyte.

Angiotensin II-stimulated collagen production in cardiac fibroblasts is mediated by reactive oxygen species

OBJECTIVE

The aim of the present study was to determine whether inhibition of reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase and of various superoxide generating systems could affect the collagen production, the mRNA and protein expression of collagen types I and III in control and angiotensin II-treated cardiac fibroblasts.

METHODS

Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency and incubated in serum-free Dulbecco's modified Eagle's medium for 24 h. The cells were then preincubated with(out) the tested inhibitors for 1 h and then further incubated with(out) angiotensin II (1 micromol/l) for 24 h. Collagen production was measured spectrophotometrically with picrosirius red as dye and with [3H]proline incorporation; collagen type I and III content by enzyme-linked immunosorbent assay and collagen type I and III mRNA expression by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). NAD(P)H-dependent superoxide anion production was assayed as superoxide dismutase-inhibitable cytochrome c reduction. Intracellular formation of reactive oxygen species was assessed with 2',7'-dichlorofluorescein diacetate as fluorescent probe.

RESULTS

Angiotensin II stimulated the collagen production, the collagen I and III content and mRNA expression in cardiac fibroblasts, and apocynin, a membrane NAD(P)H oxidase inhibitor, abolished this induction. Rotenone, allopurinol, indomethacin, nordihydroguiaretic acid, ketoconazole and nitro-L-arginine (inhibitors of mitochondrial NAD(P)H oxidase, xanthine oxidase, cyclooxygenase, lipoxygenase, cytochrome P450 oxygenase and nitric oxide synthase, respectively) did not affect the angiotensin II-induced collagen production. Angiotensin II increased the NAD(P)H-dependent superoxide anion production and the intracellular generation of reactive oxygen species in cardiac fibroblasts, and apocynin abrogated this rise.

CONCLUSIONS

Our data show that in adult rat cardiac fibroblasts the membrane-associated NAD(P)H oxidase complex is the predominant source of superoxide anion and reactive oxygen species generation in angiotensin II-stimulated adult cardiac fibroblasts. Inhibition of this NAD(P)H oxidase complex with apocynin completely blocked the angiotensin II-stimulated collagen production, and collagen I and III protein and mRNA expression.

Detection of superoxide anion generation by equine spermatozoa

OBJECTIVE

To identify the generation of the superoxide anion by equine spermatozoa.

SAMPLE POPULATION

Multiple ejaculates collected from 3 Thoroughbred stallions.

PROCEDURES

Induced superoxide production by reduced nicotinamide adenine dinucleotides (NAD[P]H; ie, reduced nicotinamide adenine dinucleotide [NADH] and reduced nicotinamide adenine dinucleotide phosphate [NADPH]) was measured by use of a nitroblue tetrazolium (NBT) reduction assay on whole spermatozoa and a cytochrome c reduction assay on isolated membrane fractions of spermatozoa. Localization of superoxide generation was determined by use of NBT cytochemistry.

RESULTS

A dose-dependent increase in NBT reduction was found in the presence of NADPH, which was inhibited by superoxide dismutase (SOD). The flavoprotein inhibitor, diphenyleneiodonium (DPI; 5 or 15 microM), significantly decreased NBT reduction. Cytochrome c reduction by plasma membranes of spermatozoa was significantly higher in the presence of NADPH than in its absence. Cytochemical staining of equine spermatozoa in the presence of NADPH and NADH revealed diaphorase labeling in the spermatozoon midpiece and head. This staining was inhibited by DPI and SOD.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of our study indicate that superoxide generation is associated with a membrane-associated NAD(P)H oxidase present in equine spermatozoa, although mitochondrial generation of superoxide is also detected. This oxidase may play a role in cell signaling or may also contribute to cytopathic effects associated with oxidative stress in equine spermatozoa.

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).

The pH dependence of NADPH oxidase in human eosinophils

NADPH oxidase generates reactive oxygen species that are essential to innate immunity against microbes. Like most enzymes, it is sensitive to pH, although the relative importance of pH(o) and pH(i) has not been clearly distinguished. We have taken advantage of the electrogenic nature of NADPH oxidase to determine its pH dependence in patch-clamped individual human eosinophils using the electron current to indicate enzyme activity. Electron current stimulated by PMA (phorbol myristate acetate) was recorded in both perforated-patch configuration, using an NH4+ gradient to control pH(i), and in excised, inside-out patches of membrane. No electron current was detected in cells or excised patches from eosinophils from a patient with chronic granulomatous disease. When the pH was varied symmetrically (pH(o) = pH(i)) in cells in perforated-patch configuration, NADPH oxidase-generated electron current was maximal at pH 7.5, decreasing drastically at higher or lower values. Varying pH(o) and pH(i) independently revealed that this pH dependence was entirely due to effects of pH(i) and that the oxidase is insensitive to pH(o). Surprisingly, the electron current in inside-out patches of membrane was only weakly sensitive to pH(i), indicating that the enzyme turnover rate per se is not strongly pH dependent. The most likely interpretation is that assembly or deactivation of the NADPH oxidase complex has one or more pH-sensitive steps, and that pH-dependent changes in electron current in intact cells mainly reflect different numbers of active complexes at different pH.

Essential role of ATF-1 in induction of NOX1, a catalytic subunit of NADPH oxidase: involvement of mitochondrial respiratory chain

NADPH oxidase is the major source of superoxide production in cardiovascular tissues. We and others reported that PG (prostaglandin) F2alpha, PDGF (platelet-derived growth factor) and angiotensin II cause hypertrophy of vascular smooth muscle cells by induction of NOX1 (NADPH oxidase 1), a catalytic subunit of NADPH oxidase. We found DPI (diphenylene iodonium), an inhibitor of flavoproteins, including NADPH oxidase itself, almost completely suppressed induction of NOX1 mRNA by PGF2alpha or PDGF in a rat vascular smooth muscle cell line, A7r5. Exploration into the site of action of DPI using various inhibitors suggested the involvement of mitochondrial oxidative phosphorylation in PGF2alpha- or PDGF-induced increase in NOX1 mRNA. In a luciferase reporter assay, activation of the CRE (cAMP-response element)-dependent gene transcription by PGF2alpha was attenuated by oligomycin, an inhibitor of mitochondrial F(o)F1-ATPase. Oligomycin and other mitochondrial inhibitors also suppressed PGF2alpha-induced phosphorylation of ATF (activating transcription factor)-1, a transcription factor of the CREB (CRE-binding protein)/ATF family. Silencing of the ATF-1 gene by RNA interference significantly reduced the induction of NOX1 by PGF2alpha or PDGF, while overexpression of ATF-1 recovered NOX1 induction suppressed by oligomycin. Taken together, ATF-1 may play a pivotal role in the up-regulation of NOX1 in rat vascular smooth muscle cells.

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.

Cigarette smoke condensate induces MMP-12 gene expression in airway-like epithelia

Cigarette smoke (CS)-induced emphysema is attributable to matrix metalloproteinase-12 (MMP-12) in mice, however, a relationship between CS and MMP-12 is absent in human emphysema. Here, we show that cigarette smoke condensate (CSC) induces MMP-12 gene expression in airway-like epithelia through a hydrogen peroxide (H(2)O(2))-dependent pathway involving NADPH oxidase, AP-1, and TNF-alpha. Cigarette smoke condensate-induced H(2)O(2) production and MMP-12 gene expression were inhibited by apocynin, a specific inhibitor of NADPH oxidases, while 3-aminobenzamide, an inhibitor of AP-1, attenuated CSC-induced MMP-12 gene expression. Messenger RNAs encoding phagocytic NADPH oxidase components and a homologue of p67phox, p51 (NOXA1), were detected, while mRNA of dual oxidase (Duox)1 was unchanged by CSC. Enbrel, an inhibitor of TNF-alpha function, reduced CSC-induced H(2)O(2) production and MMP-12 expression. These findings provide novel evidence of a direct relationship between CS exposure and MMP-12 in human airway epithelia and suggest several targets for modulation of this potentially pathogenic pathway.

Rac and Rho play opposing roles in the regulation of hypoxia/reoxygenation-induced permeability changes in pulmonary artery endothelial cells

Hypoxia/reoxygenation-induced changes in endothelial permeability are accompanied by endothelial actin cytoskeletal and adherens junction remodeling, but the mechanisms involved are uncertain. We therefore measured the activities of the Rho GTPases Rac1, RhoA, and Cdc42 during hypoxia/reoxygenation and correlated them with changes in endothelial permeability, remodeling of the actin cytoskeleton and adherens junctions, and production of ROS. Dominant negative forms of Rho GTPases were introduced into cells by adenoviral gene transfer and transfection, and inhibitors of NADPH oxidase, PI3 kinase, and Rho kinase were used to characterize the signaling pathways involved. In some experiments constitutively activated forms of RhoA and Rac1 were also used. We show for the first time that hypoxia/reoxygenation-induced changes in endothelial permeability result from coordinated actions of the Rho GTPases Rac1 and RhoA. Rac1 and RhoA rapidly respond to changes in oxygen tension, and their activity depends on NADPH oxidase- and PI3 kinase-dependent production of ROS. Rac1 acts upstream of RhoA, and its transient inhibition by acute hypoxia leads to activation of RhoA followed by stress fiber formation, dispersion of adherens junctions, and increased endothelial permeability. Reoxygenation strongly activates Rac1 and restores cortical localization of F-actin and VE-cadherin. This effect is a result of Rac1-mediated inhibition of RhoA and can be prevented by activators of RhoA, L63RhoA, and lysophosphatidic acid. Cdc42 activation follows the RhoA pattern of activation but has no effect on actin remodeling, junctional integrity, or endothelial permeability. Our results show that Rho GTPases act as mediators coupling cellular redox state to endothelial function.

Diphenyleneiodonium inhibits the cell redox metabolism and induces oxidative stress

Diphenyleneiodonium (DPI) and the structurally related compound diphenyliodonium (DIP) are widely used as inhibitors of flavoenzymes, particularly NADPH oxidase. Here we report further evidence that DPI and DIP are not specific flavin binders. A 3-h incubation of N11 glial cells with DPI significantly inhibited in a dose-dependent way both the pentose phosphate pathway and the tricarboxylic acid cycle. In parallel, we observed a dose-dependent increase of reactive oxygen species generation and lipoperoxidation and increased leakage of lactate dehydrogenase activity in the extracellular medium. The glutathione/glutathione disulfide ratio decreased, whereas the efflux of glutathione out of the cells increased. This suggests that DPI causes an augmented oxidative stress and exerts a cytotoxic effect in N11 cells. Indeed, the cells were protected from these events when loaded with glutathione. Similar results were observed using DIP instead of DPI and also in other cell types. We suggest that the DPI-elicited inhibition of the pentose phosphate pathway and tricarboxylic acid cycle may be mediated by the blockade of several NAD(P)-dependent enzymes, such as glucose 6-phosphate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase, and lactate dehydrogenase. In light of these results, we think that some effects of DPI or DIP in in vitro and in vivo experimental models should be interpreted with caution.

Reactive oxygen species mediate chloroquine-induced expression of chemokines by human astroglial cells

We have previously demonstrated that chloroquine may evoke inflammatory responses in the central nervous system by inducing expression of pro-inflammatory cytokines by astroglial cells. In this study, we further examined the molecular mechanism responsible for chloroquine-induced activation of NF-kappaB and subsequent expression of chemokines by astroglial cells. We observed that (1) chloroquine induced expression of chemokines such as CCL2 and CXCL8 in a dose- and time-dependent manner in human astroglial cells; (2) other lysosomotropic agents such as ammonium chloride and bafilomycin A1 had minimal effects on chemokine expression; (3) inhibition of NF-kappaB by MG-132 and TPCK suppressed chloroquine-induced mRNA expression of chemokines; (4) chloroquine increased the intracellular level of reactive oxygen species (ROS) in a dose- and time-dependent manner by human astroglial cells, but not by monocytic/microglial cells; (5) chloroquine-induced increase of intracellular ROS level was suppressed by pre-incubation with diphenyl iodonium (DPI) and N-acetyl cysteine (NAC); and (6) inhibition of chloroquine-induced ROS production by DPI or NAC suppressed chloroquine-mediated activation of NF-kappaB and subsequent mRNA expression of chemokines in astroglial cells. These results collectively suggest that chloroquine generates ROS, which is responsible for NF-kappaB activation and subsequent expression of pro-inflammatory chemokines in human astroglial cells.

Effect of NADPH oxidase inhibition on cardiopulmonary bypass-induced lung injury

Cardiopulmonary bypass (CPB) causes acute lung injury. Reactive oxygen species (ROS) from NADPH oxidase may contribute to this injury. To determine the role of NADPH oxidase, we pretreated pigs with structurally dissimilar NADPH oxidase inhibitors. Low-dose apocynin (4-hydroxy-3-methoxy-acetophenone; 200 mg/kg, n = 6), high-dose apocynin (400 mg/kg, n = 6), or diphenyleneiodonium (DPI; 8 mg/kg) was compared with diluent (n = 8). An additional group was treated with indomethacin (10 mg/kg, n = 3). CPB was performed for 2 h with deflated lungs, complete pulmonary artery occlusion, and bronchial artery ligation to maximize lung injury. Parameters of pulmonary function were evaluated for 25 min following CPB. Blood chemiluminescence indicated neutrophil ROS production. Electron paramagnetic resonance determined the effect of apocynin and DPI on in vitro pulmonary endothelial ROS production following hypoxia-reoxygenation. Both apocynin and DPI attenuated blood chemiluminescence and post-CPB hypoxemia. At 25 min post-CPB with Fi(O(2)) = 1, arterial Po(2) (Pa(o(2))) averaged 52 +/- 5, 162 +/- 54, 335 +/- 88, and 329 +/- 119 mmHg in control, low-dose apocynin, high-dose apocynin, and DPI-treated groups, respectively (P < 0.01). Indomethacin had no effect. Pa(O(2)) correlated with blood chemiluminescence measured after drug administration before CPB (R = -0.60, P < 0.005). Neither apocynin nor DPI prevented the increased tracheal pressure, plasma cytokine concentrations (tumor necrosis factor-alpha and IL-6), extravascular lung water, and pulmonary vascular protein permeability observed in control pigs. NADPH oxidase inhibition, but not xanthine oxidase inhibition, significantly blocked endothelial ROS generation following hypoxia-reoxygenation (P < 0.05). NADPH oxidase-derived ROS contribute to the severe hypoxemia but not to the increased cytokine generation and pulmonary vascular protein permeability, which occur following CPB.

Interactions between electron and proton currents in excised patches from human eosinophils

The NADPH–oxidase is a plasma membrane enzyme complex that enables phagocytes to generate superoxide in order to kill invading pathogens, a critical step in the host defense against infections. The oxidase transfers electrons from cytosolic NADPH to extracellular oxygen, a process that requires concomitant H⁺ extrusion through depolarization-activated H⁺ channels. Whether H⁺ fluxes are mediated by the oxidase itself is controversial, but there is a general agreement that the oxidase and H⁺ channel are intimately connected. Oxidase activation evokes profound changes in whole-cell H⁺ current (I_H), causing an approximately −40-mV shift in the activation threshold that leads to the appearance of inward I_H. To further explore the relationship between the oxidase and proton channel, we performed voltage-clamp experiments on inside-out patches from both resting and phorbol-12-myristate-13-acetate (PMA)-activated human eosinophils. Proton currents from resting cells displayed slow voltage-dependent activation, long-term stability, and were blocked by micromolar internal [Zn²⁺]. I_H from PMA-treated cells activated faster and at lower voltages, enabling sustained H⁺ influx, but ran down within minutes, regaining the current properties of nonactivated cells. Bath application of NADPH to patches excised from PMA-treated cells evoked electron currents (I_e), which also ran down within minutes and were blocked by diphenylene iodonium (DPI). Run-down of both I_H and I_e was delayed, and sometimes prevented, by cytosolic ATP and GTP-γ-S. A good correlation was observed between the amplitude of I_e and both inward and outward I_H when a stable driving force for e⁻ was imposed. Combined application of NADPH and DPI reduced the inward I_H amplitude, even in the absence of concomitant oxidase activity. The strict correlation between I_e and I_H amplitudes and the sensitivity of I_H to oxidase-specific agents suggest that the proton channel is either part of the oxidase complex or linked by a membrane-limited mediator.

Neutrophil survival on biomaterials is determined by surface topography

PURPOSE

Cardiovascular device-centered infections are a major cause of hospital morbidity, mortality, and expense. Caused by opportunistic bacteria, this phenomenon is thought to arise because of a defect in neutrophil bacterial killing. We have shown that neutrophils that adhere to polystyrene remain viable, whereas neutrophils that adhere to the vascular biomaterials expanded polytetrafluoroethylene (ePTFE) and Dacron undergo a rapid nonapoptotic death. This study was designed to test the hypothesis that surface topography is a determinant of the nonapoptotic death response of neutrophils to biomaterials.

METHODS

We took advantage of the ease with which a polystyrene surface can be manipulated to examine the effect of surface topography on neutrophil viability. Neutrophils were exposed to smooth or roughened polystyrene surfaces both in vivo and in vitro. Changes in cell membrane permeability and production of reactive oxygen species by individual cells were monitored with fluorescent dyes.

RESULTS

Host cells and isolated human neutrophils died rapidly after adhesion to roughened polystyrene. Neutrophils adherent to roughened surfaces produced more reactive oxygen intermediates than those adherent to smooth surfaces and were first to die. The cell death response precipitated by expanded polytetrafluoroethylene, Dacron, or the roughened surfaces was significantly reduced with treatment of the neutrophils with catalase, diphenylene iodonium, or the src kinase inhibitor PP2 before adhesion.

CONCLUSIONS

Neutrophil adhesion to roughened materials triggers rapid production of reactive oxygen species and precipitates a nonapoptotic cell death. Understanding the material properties that trigger these responses is essential to development of the next generation of implantable biomaterials.

Diphenyleneiodonium triggers the efflux of glutathione from cultured cells

Diphenyleneiodonium (DPI) is a broad-spectrum flavoprotein inhibitor commonly used to inhibit oxidant production by the NADPH oxidase of phagocytic and nonphagocytic cells. A previous study has shown that DPI can sensitize T24 bladder carcinoma cells to Fas-mediated apoptosis. We observed DPI to deplete intracellular reduced glutathione (GSH) in T24 cells and a range of other primary and transformed cell types. The effect was immediate, with 50% loss of intracellular GSH within 2 h of treatment with DPI. The glutathione was quantitatively recovered in the extracellular medium, indicating that efflux was occurring. The loss of GSH was blocked with bromosulfophthalein, an inhibitor of the canalicular GSH transporters. We conclude that DPI induces a dramatic efflux of cellular GSH from T24 cells via a specific transport channel. This provides a potential mechanism for its proapoptotic effect, and it also has important implications for the regulation of glutathione homeostasis in cells.

Exploration of the diaphorase activity of neutrophil NADPH oxidase

In the O2- generating flavocytochrome b, the membrane-bound component of the neutrophil NADPH oxidase, electrons are transported from NADPH to O2 in the following sequence: NADPH --> FAD --> heme b -->O2. Although p-iodonitrotetrazolium (INT) has frequently been used as a probe of the diaphorase activity of the neutrophil flavocytochrome b, the propensity of its radical to interact reversibly with O2 led us to question its specificity. This study was undertaken to reexamine the interaction of INT with the redox components of the neutrophil flavocytochrome b. Two series of inhibitors were used, namely the flavin analog 5-deaza FAD and the heme inhibitors bipyridyl and benzylimidazole. The following results indicate that INT reacts preferentially with the hemes rather than with the FAD redox center of flavocytochrome b and is not therefore a specific probe of the diaphorase activity of flavocytochrome b. First, in anaerobiosis, reduced heme b in activated membranes was reoxidized by INT as efficiently as by O2 even in the presence of concentrations of 5-deaza FAD which fully inhibited the NADPH oxidase activity. Second, the titration curve of dithionite-reduced heme b in neutrophil membranes obtained by oxidation with increasing amounts of INT was strictly superimposable on that of dithionite-reduced hemin. Third, INT competitively inhibited the O2 uptake by the activated NADPH oxidase in a cell-free system. Finally, the heme inhibitor bipyridyl competitively inhibited the reduction of INT in anaerobiosis, and the oxygen uptake in aerobiosis.

Effect of a high-salt diet on oxidant enzyme activity in skeletal muscle microcirculation

Increased salt intake attenuates the endothelium-dependent dilation of skeletal muscle arterioles by abolishing local nitric oxide (NO) activity. There is evidence of oxidative stress in arteriolar and venular walls of rats fed a high-salt diet, and depressed arteriolar responses to acetylcholine (ACh) in these rats are reversed by scavengers of reactive oxygen species (ROS). In this study, we tested the hypothesis that this salt-dependent increase in microvascular ROS and the resulting attenuation of endothelium-dependent dilation are due to increased expression and/or activity of oxidant enzymes in the microvascular wall. Resting arteriolar and venular wall oxidant activity, as assessed by tetranitroblue tetrazolium reduction, was consistently higher in the spinotrapezius muscle of rats fed a high-salt diet (7% NaCl, HS) for 4-5 wk than in those fed a normal diet (0.45% NaCl, NS) for the same duration. Western analysis of protein from isolated microvessels showed no difference between HS and NS rats in the expression of NAD(P)H oxidase or xanthine oxidase. Inhibition of NAD(P)H oxidase and/or xanthine oxidase with diphenyleneiodonium chloride and oxypurinol, respectively, reduced resting arteriolar wall oxidant activity to normal levels in HS rats but had no effect in NS rats, suggesting that the basal activities of NAD(P)H oxidase and xanthine oxidase are increased in HS microvessels. However, inhibition of these enzymes in HS rats did not restore normal arteriolar responses to ACh, suggesting that this stimulus activates an alternate source of ROS that eliminates the role of NO in the subsequent dilation.

Inhibition of NADH/NADPH oxidase affects signal transduction by growth factor receptors in normal fibroblasts

Reactive oxygen species have been implicated as possible second messengers in mitogenic signal transduction. We demonstrate that in normal fibroblasts the treatment with the two inhibitors of phagocytic NADH/NADPH oxidase prevents tyrosine phosphorylation of platelet-derived growth factor receptor upon the exposure of serum-deprived cells to growth factors. Furthermore, the inhibition of NADH/NADPH oxidase abolishes ERKs activation and p21(waf1) accumulation that occurs when cells are exposed to growth factors. Finally, NADH/NADPH inhibitors prevent the p66(Shc) Ser-phosphorylation induced by serum and by phorbol 12-myristate-13-acetate, which suggests that the direct target(s) of reactive oxygen species is(are) located upstream from the machinery connecting growth factor receptors to Ras.

Essential requirement of cytosolic phospholipase A(2) for stimulation of NADPH oxidase-associated diaphorase activity in granulocyte-like cells

We have previously established a model of cytosolic phospholipase A(2) (cPLA(2))-deficient differentiated PLB-985 cells (PLB-D cells) and demonstrated that cPLA(2)-generated arachidonic acid (AA) is essential for NADPH oxidase activation. In this study we used this model to investigate the physiological role of cPLA(2) in regulation of NADPH oxidase-associated diaphorase activity. A novel diaphorase activity assay, using 4-iodonitrotetrazolium violet as an electron acceptor, was used in permeabilized neutrophils and PLB-985 cells differentiated toward the granulocytic or monocytic phenotypes. Phorbol 12-myristate 13-acetate, guanosine 5'-3-O- (thio)triphosphate (GTP gamma S), or FMLP stimulated a similar diphenylene iodonium-sensitive diaphorase activity pattern in neutrophils and in differentiated parent PLB-985 cells. This diaphorase activity was not detected in undifferentiated cells, but developed during differentiation. Furthermore, diaphorase activity could not be stimulated in permeabilized neutrophils from X-linked CGD patients and in differentiated gp91(phox)-targeted PLB-985 cells that lacked normal expression of gp91(phox), but was restored to these cells following transduction with retrovirus encoding gp91(phox). The differentiated PLB-D cells showed no diaphorase activity when stimulated by either GTP gamma S or FMLP, and only partial activation when stimulated with phorbol 12-myristate 13-acetate. Diaphorase activity in response to either agonists was fully restored by the addition of 10 microm free AA. The permeabilized cell 4-iodonitrotetrazolium violet reduction assay offers a unique tool for the evaluation of NADPH oxidase-associated diaphorase activity in stimulated whole cells. These results establish an essential and specific physiological requirement of cPLA(2)-generated AA in activation of electron transfer through the FAD reduction center of NADPH oxidase.

Novel competitive inhibitor of NAD(P)H oxidase assembly attenuates vascular O(2)(-) and systolic blood pressure in mice

We previously reported enhanced expression of the p67(phox) and gp91(phox) components of NAD(P)H oxidase in angiotensin (Ang) II-induced hypertension, suggesting de novo assembly in response to Ang II. To examine the direct involvement of NAD(P)H oxidases in Ang II-induced O(2)(-) production, we designed a chimeric peptide that inhibits p47(phox) association with gp91(phox) in NAD(P)H oxidase (gp91ds-tat). This was achieved by linking a 9-amino acid peptide (aa) derived from HIV-coat protein (tat) to a 9-aa sequence of gp91(phox) (known to interact with p47(phox)). As a control, we constructed a chimera containing tat and a scrambled gp91 sequence (scramb-tat). We found that gp91ds-tat decreased O(2)(-) levels in aortic rings treated with Ang II (10 pmol/L) but had no effect on either the O(2)(-)-generating enzyme xanthine oxidase or potassium superoxide-generated O(2)(-). We infused vehicle, Ang II (0.75 mg. kg(-1). d(-1)), Ang II+gp91ds-tat (10 mg. kg(-1). d(-1)), or Ang II+scramb-tat intraperitoneally in C57Bl/6 mice and measured systolic blood pressure (SBP) on days 0, 3, 5, and 7 of infusion. SBP increased by day 3 in mice given Ang II and Ang II+scramb-tat but was significantly lower with Ang II+gp91-tat. On day 7, SBP was still significantly inhibited in mice given Ang II+gp91ds-tat, whereas Ang II-induced O(2)(-) production was inhibited throughout the aorta as detected by dihydroethidium staining, consistent with the ability of this inhibitor to block the various vascular NAD(P)H oxidase isoforms. These data support the hypothesis that inhibition of the interaction of p47(phox) and gp91(phox) (or its homologues) can block O(2)(-) production and attenuate blood pressure elevation in mice.

Genetic demonstration of p47phox-dependent superoxide anion production in murine vascular smooth muscle cells

BACKGROUND

Previous investigations provide evidence that an enzyme related to the phagocyte NADPH oxidase produces superoxide in the blood vessel wall. These data, however, are confounded by observations that both NADPH and NADH serve as substrates for superoxide production in vascular cells. To clarify this issue, we compared the superoxide-generating capabilities of vascular smooth muscle cells (VSMCs) derived from wild-type (p47phox(+/+); phagocyte oxidase) mice with those from mice that lack p47phox (p47phox(-/-); "knockout"), an essential component of the phagocyte NADPH oxidase.

METHODS AND RESULTS

VSMCs were derived from aortic explants harvested from p47phox(+/+) or p47phox(-/-) mice. VSMCs from p47phox(+/+) but not those from p47phox(-/-) mice produced superoxide after stimulation by phorbol myristate acetate. Consistent with this, p47phox was detected only in p47phox(+/+) VSMCs. p47phox-transduced p47phox(-/-) but not enhanced green fluorescent protein-transduced p47phox(-/-) VSMCs generated significant levels of superoxide after stimulation by angiotensin II or platelet-derived growth factor-BB (PDGF-BB). Enhanced expression of recombinant p47phox in p47phox-transduced p47phox(-/-) cells correlated with superoxide production in these cells.

CONCLUSIONS

These data provide direct functional proof that an oxidase requiring the p47phox component mediates superoxide release from VSMCs in the blood vessel wall in response to angiotensin II or PDGF-BB.

Electron spin resonance characterization of the NAD(P)H oxidase in vascular smooth muscle cells

Endogenously produced reactive oxygen species are important for intracellular signaling mechanisms leading to vascular smooth muscle cell (VSMC) growth. It is therefore critical to define the potential enzymatic sources of ROS and their regulation by agonists in VSMCs. Previous studies have investigated O2*- production using lucigenin-enhanced chemiluminescence. However, lucigenin has been recently criticized for its ability to redox cycle and its propensity to measure cellular reductase activity independent from O2*-. To perform a definitive characterization of VSMC oxidase activity, we used electron spin resonance trapping of O2*- with DEPMPO. We confirmed that the main source of O2*- from VSMC membranes is an NAD(P)H oxidase and that the O2*- formation from mitochondria, xanthine oxidase, arachidonate-derived enzymes, and nitric oxide synthases in VSMC membranes was minor. The VSMC NAD(P)H oxidase(s) are able to produce more O2*- when NADPH is used as the substrate compared to NADH (the maximal NADPH signal is 2.4- +/- 0.4-fold higher than the NADH signal). The two substrates had similar EC(50)'s ( approximately 10-50 microM). Stimulation with angiotensin II and platelet-derived growth factor also predominantly increased the NADPH-driven signal (101 +/- 8% and 83 +/- 1% increase above control, respectively), with less of an effect on NADH-dependent O2*- (17 +/- 3% and 36 +/- 5% increase, respectively). Moreover, incubation of the cells with diphenylene iodonium inhibited predominantly NADPH-stimulated O2*-. In conclusion, electron spin resonance characterization of VSMC oxidase activity supports a major role for an NAD(P)H oxidase in O2*- production in VSMCs, and provides new evidence concerning the substrate dependency and agonist-stimulated activity of this key enzyme.

A new superoxide-generating oxidase in murine osteoclasts

Superoxide production contributes to osteoclastic bone resorption. Evidence strongly indicates that NADPH oxidase is an enzyme system responsible for superoxide generation in osteoclasts. A membrane-bound subunit, p91, is the catalytic domain of NADPH oxidase. However, osteoclasts from p91 knockout mice still produce superoxide at a rate similar to that observed in wild type mice. This unexpected phenomenon prompted us to examine the osteoclasts for an alternative to the p91-containing oxidase. In this study, the cloning of a NADPH oxidase subunit (Nox 4) with 578 amino acids is reported. Nox 4 has 58% similarity in amino acids with the known p91 subunit of NADPH oxidase. Nox 4 is present and active in osteoclasts. Antisense oligonucleotides of Nox 4 reduced osteoclastic superoxide generation as well as resorption pit formation by osteoclasts. This new oxidase complex was present and functional in osteoclasts from p91 knockout mice, explaining the normal resorptive activity seen in the osteoclasts where no p91 is present.

Genetic requirement of p47phox for superoxide production by murine microglia

An NADPH oxidase is thought to function in microglial cells of the central nervous system. These conclusions are based on pharmacological and immunochemical evidence, although these approaches are indirect and raise issues of specificity. For example, diphenyleneiodonium inhibits a variety of flavoenzymes, including xanthine oxidase, NADH dehydrogenase, and NADPH oxidase. Here, we provide genetic evidence that p47phox, an essential component of the phagocyte NADPH oxidase, is required for superoxide anion release from microglia. Microglia derived from newborn wild-type mice, but not from newborn p47phox-deficient (knockout; -/-) mice, produced superoxide after stimulation by opsonized zymosan or phorbol myristate acetate. Endogenous p47phox was detected only in wild-type microglia, consistent with selective superoxide production in these cells. Superoxide release was restored in p47phox-deficient microglia that were retrovirally transduced with human p47phox cDNA. Similar kinetics of superoxide generation were observed, consistent with the same enzyme functioning in wild-type and restored microglia. Immuno-detection of p47phox in transduced cells confirmed that restoration of superoxide release correlated with production of recombinant protein. These data provide genetic proof that p47phox is necessary for superoxide release by microglial cells and indicate that a system related to the phagocyte oxidase is active in these cells.

Characterization of the intramolecular electron transfer pathway from 2-hydroxyphenazine to the heterodisulfide reductase from Methanosarcina thermophila

Heterodisulfide reductase (HDR) is a component of the energy-conserving electron transfer system in methanogens. HDR catalyzes the two-electron reduction of coenzyme B-S-S-coenzyme M (CoB-S-S-CoM), the heterodisulfide product of the methyl-CoM reductase reaction, to free thiols, HS-CoB and HS-CoM. HDR from Methanosarcina thermophila contains two b-hemes and two [Fe(4)S(4)] clusters. The physiological electron donor for HDR appears to be methanophenazine (MPhen), a membrane-bound cofactor, which can be replaced by a water-soluble analog, 2-hydroxyphenazine (HPhen). This report describes the electron transfer pathway from reduced HPhen (HPhenH(2)) to CoB-S-S-CoM. Steady-state kinetic studies indicate a ping-pong mechanism for heterodisulfide reduction by HPhenH(2) with the following values: k(cat) = 74 s(-1) at 25 degrees C, K(m) (HPhenH(2)) = 92 microm, K(m) (CoB-S-S-CoM) = 144 microm. Rapid freeze-quench EPR and stopped-flow kinetic studies and inhibition experiments using CO and diphenylene iodonium indicate that only the low spin heme and the high potential FeS cluster are involved in CoB-S-S-CoM reduction by HPhenH(2). Fe-S cluster disruption by mersalyl acid inhibits heme reduction by HPhenH(2), suggesting that a 4Fe cluster is the initial electron acceptor from HPhenH(2). We propose the following electron transfer pathway: HPhenH(2) to the high potential 4Fe cluster, to the low potential heme, and finally, to CoB-S-S-CoM.

Human placental NAD(P)H oxidase: solubilization and properties

The NAD(P)H oxidase in the syncytiotrophoblast of the term human placenta, which had previously been identified only by cytochemical methods, has been solubilized and a number of its biochemical properties have been defined. It is a protein composed of a 58 kDa and a 33 kDa subunit, with properties that clearly distinguish it from the respiratory burst oxidase of transient neutrophils and macrophages. The enzyme activity is constitutive in the trophoblast and is a source of reactive oxygen species (ROS) at the fetal-maternal interface.

The inhibition of flavoproteins by phenoxaiodonium, a new iodonium analogue

Iodonium compounds, especially diphenylene iodonium and iodonium diphenyl are used extensively as inhibitors of NADH-ubiquinone reductase and NADPH oxidase activity. Here, the use of a new iodonium compound, phenoxaiodonium is reported. The IC(50) of neutrophil superoxide production, measured using the superoxide dismutase inhibitable rate of cytochrome c reduction, was approximately 0.75 microM, while 50% inhibition of mitochondrial respiration, measured by the rate of oxygen uptake using a Clark type oxygen electrode, was at approximately 20 microM. The inhibition of oxidation of xanthine to urate by xanthine oxidase was also studied, giving a K(i) of 0.2 microM. Inhibition of nitric oxidase synthase (NOS: from rat brain) by 0.2 microM phenoxaiodonium was equivalent to 1 mM N(G)-nitro-L-arginine methyl ester HCl (L-NAME), that is total abolition of activity. We conclude that phenoxaiodonium is an extremely good inhibitor of flavo-enzymes, but like diphenylene iodonium and iodonium diphenyl, will be of limited use as a pharmacological tool for the elucidation of the involvement of such enzymes in specific cellular functions.

Diphenylene iodonium as an inhibitor for the hydrogenase complex of Rhodobacter capsulatus. Evidence for two distinct electron donor sites

The photosynthetic bacterium Rhodobacter capsulatus synthesises a membrane-bound [NiFe] hydrogenase encoded by the H2 uptake hydrogenase (hup)SLC structural operon. The hupS and hupL genes encode the small and large subunits of hydrogenase, respectively; hupC encodes a membrane electron carrier protein which may be considered as the third subunit of the uptake hydrogenase. In Wolinella succinogenes, the hydC gene, homologous to hupC, has been shown to encode a low potential cytochrome b which mediates electron transfer from H2 to the quinone pool of the bacterial membrane. In whole cells of R. capsulatus or intact membrane preparation of the wild type strain B10, methylene blue but not benzyl viologen can be used as acceptor of the electrons donated by H2 to hydrogenase; on the other hand, membranes of B10 treated with Triton X-100 or whole cells of a HupC- mutant exhibit both benzyl viologen and methylene blue reductase activities. We report the effect of diphenylene iodonium (Ph2I), a known inhibitor of mitochondrial complex I and of various monooxygenases on R. capsulatus hydrogenase activity. With H2 as electron donor, Ph2I inhibited partially the methylene blue reductase activity in an uncompetitive manner, and totally benzyl viologen reductase activity in a competitive manner. Furthermore, with benzyl viologen as electron acceptor, Ph2I increased dramatically the observed lagtime for dye reduction. These results suggest that two different sites exist on the electron donor side of the membrane-bound [NiFe] hydrogenase of R. capsulatus, both located on the small subunit. A low redox potential site which reduces benzyl viologen, binds Ph2I and could be located on the distal [Fe4S4] cluster. A higher redox potential site which can reduce methylene blue in vitro could be connected to the high potential [Fe3S4] cluster and freely accessible from the periplasm.

Effect of the NADPH oxidase inhibitor apocynin on ischemia-reperfusion lung injury

Apocynin (4-hydroxy-3-methoxy-acetophenone) inhibits NADPH oxidase in activated polymorphonuclear (PMN) leukocytes, preventing the generation of reactive oxygen species. To determine if apocynin attenuates ischemia-reperfusion lung injury, we examined the effects of apocynin (0.03, 0.3, and 3 mM) in isolated in situ sheep lungs. In diluent-treated lungs, reperfusion with blood (180 min) after 30 min of ischemia (ventilation 28% O(2), 5% CO(2)) caused leukocyte sequestration in the lung and increased vascular permeability [reflection coefficient for albumin (sigma(alb)) 0.47 +/- 0.10, filtration coefficient (K(f)) 0.14 +/- 0.03 g. min(-1). mmHg(-1). 100 g(-1)] compared with nonreperfused lungs (sigma(alb) 0.77 +/- 0. 03, K(f) 0.03 +/- 0.01 g. min(-1). mmHg(-1). 100 g(-1); P < 0.05). Apocynin attenuated the increased protein permeability at 0.3 and 3 mM (sigma(alb) 0.69 +/- 0.05 and 0.91 +/- 0.03, respectively, P < 0. 05); K(f) was decreased by 3 mM apocynin (0.05 +/- 0.01 g. min(-1). mmHg(-1). 100 g(-1), P < 0.05). Diphenyleneiodonium (DPI, 5 microM), a structurally unrelated inhibitor of NADPH oxidase, worsened injury (K(f) 0.32 +/- 0.07 g. min(-1). mmHg(-1). 100 g(-1), P < 0.05). Neither apocynin nor DPI affected leukocyte sequestration. Apocynin and DPI inhibited whole blood chemiluminescence and isolated PMN leukocyte-induced resazurin reduction, confirming NADPH oxidase inhibition. Apocynin inhibited pulmonary artery hypertension and perfusate concentrations of cyclooxygenase metabolites, including thromboxane B(2). The cyclooxygenase inhibitor indomethacin had no effect on the increased vascular permeability, suggesting that cyclooxygenase inhibition was not the explanation for the apocynin results. Apocynin prevented ischemia-reperfusion lung injury, but the mechanism of protection remains unclear.

Transcriptional activation of the human manganese superoxide dismutase gene mediated by tetradecanoylphorbol acetate

Transcriptional activation of human manganese superoxide dismutase (MnSOD) mRNA induced by a phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), was examined to identify the responsive transcriptional regulator. The effect of various deletions and mutations within the 5'-flanking region of the human MnSOD gene promoter was evaluated using the luciferase reporter system in A549 human lung carcinoma cells. Deletion of a region between -1292 and -1202 nucleotides upstream of the transcription start site abolished TPA-responsive induction, whereas deletion of the putative binding sequence for NF-kappaB or AP-1 did not. The region between -1292 and -1202 contains a cAMP-responsive element-like sequence, TGACGTCT, which we identified as the manganese superoxide dismutase TPA-responsive element, MSTRE. Site-specific mutation of the MSTRE abolished the TPA-responsive induction, validating the critical role of this sequence. We detected specific MSTRE activity from nuclear extracts and demonstrated by antibody supershift assay that this activity is closely related to CREB-1/ATF-1. TPA treatment rapidly induced phosphorylation of the CREB-1/ATF-1-like factor via the protein kinase C pathway. These results led us to conclude that the human MnSOD gene having the promoter construct used in this study is induced by TPA via activation of a CREB-1/ATF-1-like factor and not via either NF-kappaB or AP-1. In addition, we found that this induction was blocked by inhibitors of flavoproteins and NADPH oxidases, indicating involvement of enhanced generation of superoxide radical anion as an upstream signal.

Does diphenylene iodonium chloride have any effect on the O2- -generating step of plant peroxidases?

The O2*- -generating step of plant peroxidases during their catalytic cycle is represented by the decay of compound III (CoIII) into ferriperoxidase, which most likely involves the dissociation of a ferric-O2*- complex to yield the ferric form of the enzyme and O2*-. Diphenylene iodonium chloride (DPI), at 50-100 microM, does not significantly enhance the stability of CoIII of peroxidase, as judged by the values of k(decay), and therefore, DPI appears to have no effect on the O2*- -generating step of plant peroxidases. From these results, it is concluded that caution should be exercised when considering peroxidase as a possible enzyme target of O2*- -mediated plant physiological processes sensitive to DPI inhibition.

Redox regulation of beta2-integrin CD11b/CD18 activation

Although the central role of beta2-integrin CD11b / CD18 in neutrophil functions is well recognized, signaling pathway that regulate integrin activation remain to be elucidated. We analyzed the contribution of oxido-reduction mechanisms in this signaling. Exogenously added H(2)O(2) induced CD11b/CD18-dependent neutrophil adhesion and expression of an integrin activation neoepitope recognized by monoclonal antibody (mAb) clone 24. H(2)O(2)-triggered beta2-integrin activation was inhibited by tyrosine kinase inhibitors and by complexing sulfhydryl groups with phenylarsine oxide (PAO). CD11b/CD18-dependent adhesion and mAb 24 antigen expression triggered by physiological agonists such as TNF-alpha were inhibited by diphenylene iodonium (DPI, an inhibitor of flavoprotein oxidoreductase), by free radical scavengers, by tyrosine kinase inhibitors and by PAO. No inhibition was observed when adhesion was induced by the integrin-activating KIM 185 mAb. Taken together, these results emphasize the importance of an oxidative S-thiolation step(s) in the tyrosine kinase-dependent signaling pathway leading to beta2-integrin activation. H(2)O(2) would directly mediate this oxidative reaction and bypass the initial agonist/receptor pathway to promote integrin-dependent adhesion. The putative oxidase(s) involved in this process is not NADPH oxidase, since adhesion of neutrophils from patients with chronic granulomatous disease was normal and inhibited by scavengers and DPI. These data shed a new light on the regulation of integrin activation required for cell migration into inflamed organs.

Yersinia pseudotuberculosis blocks the phagosomal acidification of B10.A mouse macrophages through the inhibition of vacuolar H(+)-ATPase activity

Yersinia pseudotuberculosis survived and multiplied in the phagosomes of B10.A mouse peritoneal macrophages. As one of the possible mechanisms for the bacteria's survival in the phagosomes, we demonstrated that live Y. pseudotuberculosis inhibited the phagosomal acidification; pH within phagosomes containing the live Y. pseudotuberculosis remained at about 6.0, whereas pH within phagosomes containing the dead Y. pseudotuberculosis fell to about 4. 5. This ability to inhibit intraphagosomal acidification was also shared by mutants lacking the 42 Md virulence plasmid, indicating that it is chromosomally encoded. The phagosomes containing dead bacteria raised the pH to 6.2 after the treatment of their macrophages with an inhibitor (bafilomycin A1) specific for V-ATPase. Although the amount of V-ATPase in the A and B subunits on the phagosomes was not significantly different between the live and dead bacteria infection, the phagosomes containing live bacteria had a 10-fold smaller V-ATPase activity than those containing the dead bacteria. These results indicated that the inhibition of phagosomal acidification by Y. pseudotuberculosis infection was due to the attenuation of V-ATPase activity, and not due to the exclusion of V-ATPase subunits from the phagosome membrane as found in Mycobacterium avium.

Shear-induced tyrosine phosphorylation in endothelial cells requires Rac1-dependent production of ROS

The shear-induced intracellular signal transduction pathway in vascular endothelial cells involves tyrosine phosphorylation and activation of mitogen-activated protein (MAP) kinase, which may be responsible for the sustained release of nitric oxide. MAP kinase is known to be activated by reactive oxygen species (ROS), such as H2O2, in several cell types. ROS production in ligand-stimulated nonphagocytic cells appears to require the participation of a Ras-related small GTP-binding protein, Rac1. We hypothesized that Rac1 might serve as a mediator for the effect of shear stress on MAP kinase activation. Exposure of bovine aortic endothelial cells to laminar shear stress of 20 dyn/cm2 for 5-30 min stimulated total cellular and cytosolic tyrosine phosphorylation as well as tyrosine phosphorylation of MAP kinase. Treating endothelial cells with the antioxidants N-acetylcysteine and pyrrolidine dithiocarbamate inhibited in a dose-dependent manner the shear-stimulated increase in total cytosolic and, specifically, MAP kinase tyrosine phosphorylation. Hence, the onset of shear stress caused an enhanced generation of intracellular ROS, as evidenced by an oxidized protein detection kit, which were required for the shear-induced total cellular and MAP kinase tyrosine phosphorylation. Total cellular and MAP kinase tyrosine phosphorylation was completely blocked in sheared bovine aortic endothelial cells expressing a dominant negative Rac1 gene product (N17rac1). We concluded that the GTPase Rac1 mediates the shear-induced tyrosine phosphorylation of MAP kinase via regulation of the flow-dependent redox changes in endothelial cells in physiological and pathological circumstances.

The heme component of the neutrophil NADPH oxidase complex is a target for aryliodonium compounds

The redox core of the neutrophil NADPH oxidase complex is a membrane-bound flavocytochrome b in which FAD and heme b are the two prosthetic redox groups. Both FAD and heme b are able to react with diphenylene iodonium (DPI) and iodonium biphenyl (IBP), two inhibitors of NADPH oxidase activity. In this study, we show that the iodonium modification of heme b contributes predominantly to the inhibition of NADPH oxidase. This conclusion is based on the finding that both iodonium compounds decreased the absorbance of the Soret peak of flavocytochrome b in neutrophil membranes incubated with NADPH, and that this decrease was strictly correlated with the loss of oxidase activity. Furthermore, the heme component of purified flavocytochrome b reduced to no more than 95% by a limited amount of sodium dithionite could be oxidized by DPI or IBP. Butylisocyanide which binds to heme iron precludes heme b oxidation. In activated neutrophil membranes, competitive inhibition of O2 uptake by DPI or IBP occurred transiently and was followed by a noncompetitive inhibition. These results, together with those of EPR spectroscopy experiments, lead us to postulate that DPI or IBP first captures an electron from the reduced heme iron of flavocytochrome b to generate a free radical. Then, the binding of this radical to the proximate environment of the heme iron, most probably on the porphyrin ring, results in inhibition of oxidase activity. In the presence of an excess of sodium dithionite, DPI and IBP produced a biphasic decrease of the Soret band of flavocytochrome b, with a break in the dose effect curve occurring at 50% of the absorbance loss. This was consistent with the presence of two hemes in flavocytochrome b that differ by their sensitivity to DPI or IBP.

NADPH oxidase inhibition does not interfere with low PO2 transduction in rat and rabbit CB chemoreceptor cells

The aim of the present work was to elucidate the role of NADPH oxidase in hypoxia sensing and transduction in the carotid body (CB) chemoreceptor cells. We have studied the effects of several inhibitors of NADPH oxidase on the normoxic and hypoxia-induced release of [3H]catecholamines (CA) in an in vitro preparation of intact CB of the rat and rabbit whose CA deposits have been labeled by prior incubation with the natural precursor [3H]tyrosine. It was found that diphenyleneiodonium (DPI; 0.2-25 microM), an inhibitor of NADPH oxidase, caused a dose-dependent release of [3H]CA from normoxic CB chemoreceptor cells. Contrary to hypoxia, DPI-evoked release was only partially Ca2+ dependent. Concentrations of DPI reported to produce full inhibition of NADPH oxidase in the rat CB did not prevent the hypoxic release response in the rat and rabbit CB chemoreceptor cells, as stimulation with hypoxia in the presence of DPI elicited a response equaling the sum of that produced by DPI and hypoxia applied separately. Neopterin (3-300 microM) and phenylarsine oxide (0.5-2 microM), other inhibitors of NADPH oxidase, did not promote release of [3H]CA in normoxic conditions or affect the response elicited by hypoxia. On the basis of effects of neopterin and phenylarsine oxide, it is concluded that NADPH oxidase does not appear to play a role in oxygen sensing or transduction in the rat and rabbit CB chemoreceptor cells in vitro and, in the context of the present study, that DPI effects are not related to NADPH oxidase inhibition.

Enantioselective inhibition of the biotransformation and pharmacological actions of isoidide dinitrate by diphenyleneiodonium sulphate

1. We have shown previously that the D- and L- enantiomers of isoidide dinitrate (D-IIDN and L-IIDN) exhibit a potency difference for relaxation and cyclic GMP accumulation in isolated rat aorta and that this is related to preferential biotransformation of the more potent enantiomer (D-IIDN). The objective of the current study was to examine the effect of the flavoprotein inhibitor, diphenyleneiodonium sulphate (DPI), on the enantioselectivity of IIDN action. 2. In isolated rat aortic strip preparations, exposure to 0.3 microM DPI resulted in a 3.6 fold increase in the EC50 value for D-IIDN-induced relaxation, but had no effect on L-IIDN-induced relaxation. 3. Incubation of aortic strips with 2 microM D- or L-IIDN for 5 min resulted in significantly more D-isoidide mononitrate formed (5.0 +/- 1.5 pmol mg protein(-1)) than L-isoidide mononitrate (2.1 +/- 0.7 pmol mg protein(-1)) and this difference was abolished by pretreatment of tissues with 0.3 microM DPI. DPI had no effect on glutathione S-transferase (GST) activity or GSH-dependent biotransformation of D- or L-IIDN in the 105,000 x g supernatant fraction of rat aorta. 4. Consistent with both the relaxation and biotransformation data, treatment of tissues with 0.3 microM DPI significantly inhibited D-IIDN-induced cyclic GMP accumulation, but had no effect on L-IIDN-induced cyclic GMP accumulation. 5. In the intact animal, 2 mg kg(-1) DPI significantly inhibited the pharmacokinetic and haemodynamic properties of D-IIDN, but had no effect L-IIDN. 6. These data suggest that the basis for the potency difference for relaxation by the two enantiomers is preferential biotransformation of D-IIDN to NO, by an enzyme that is inhibited by DPI. Given that DPI binds to and inhibits NADPH-cytochrome P450 reductase, the data are consistent with a role for the cytochromes P450-NADPH-cytochrome P450 reductase system in this enantioselective biotransformation process.

Inhibition of membrane-bound electron transport of the methanogenic archaeon Methanosarcina mazei Gö1 by diphenyleneiodonium

The proton translocating electron transport systems (F420H2:heterodisulfide oxidoreductase and H2:heterodisulfide oxidoreductase) of Methanosarcina mazei Gö1 were inhibited by diphenyleneiodonium chloride (DPI) indicated by IC50 values of 20 nmol DPI.mg-1 protein and 45 nmol DPI.mg-1 protein, respectively. These effects are due to a complex interaction of DPI with key enzymes of the electron transport chains. It was found that 2-hydroxyphenazine-dependent reactions as catalyzed by F420-nonreducing hydrogenase, F420H2 dehydrogenase and heterodisulfide reductase were inhibited. Interestingly, the H2-dependent methylviologen reduction and the heterodisulfide reduction by reduced methylviologen as catalyzed by the hydrogenase and the heterodisulfide reductase present in washed membranes were unaffected by DPI, respectively. Analysis of the redox behavior of membrane-bound cytochromes indicated that DPI inhibited CoB-S-S-CoM-dependent oxidation of reduced cytochromes and H2-dependent cytochrome reduction. Membrane-bound and purified F420H2 dehydrogenase were inhibited by DPI irrespectively whether methylviologen + metronidazole or 2-hydroxyphenazine were used as electron acceptors. Detailed examination of 2-hydroxy-phenazine-dependent F420H2-oxidation revealed that DPI is a competitive inhibitor of the enzyme, indicated by the Km value for 2-hydroxyphenazine, which increased from 35 microm to 100 microm in the presence of DPI. As DPI and phenazines are structurally similar with respect to their planar configuration we assume that the inhibitor is able to bind to positions where interaction between phenazines and components of the electron transport systems take place. Thus, electron transfer from reduced 2-hydroxyphenazine to cytochrome b2 as part of the heterodisulfide reductase and from H2 to cytochrome b1 as subunit of the membrane-bound hydrogenase is affected in the presence of DPI. In case of the F420H2 dehydrogenase electron transport from FAD or from FeS centers to 2-hydroxyphenazine is inhibited.

The respiratory burst and electrolyte leakage induced by sulfhydryl blockers in egeria densa leaves are associated with H2O2 production and are dependent on Ca2+ influx

In leaves of Egeria densa Planchon, N-ethylmaleimide (NEM) and other sulfhydryl-binding reagents induce a temporary increase in nonmitochondrial respiration (DeltaQO2) that is inhibited by diphenylene iodonium and quinacrine, two known inhibitors of the plasma membrane NADPH oxidase, and are associated with a relevant increase in electrolyte leakage (M. Bellando, S. Sacco, F. Albergoni, P. Rocco, M.T. Marre [1997] Bot Acta 110: 388-394). In this paper we report data indicating further analogies between the oxidative burst induced by sulfhydryl blockers in E. densa and that induced by pathogen-derived elicitors in animal and plant cells: (a) NEM- and Ag+-induced DeltaQO2 was associated with H2O2 production and both effects depended on the presence of external Ca2+; (b) Ca2+ influx was markedly increased by treatment with NEM; (c) the Ca2+ channel blocker LaCl3 inhibited DeltaQO2, electrolyte release, and membrane depolarization induced by the sulfhydryl reagents; and (d) LaCl3 also inhibited electrolyte leakage induced by the direct infiltration of the leaves with H2O2. These results suggest a model in which the interaction of sulfhydryl blockers with sulfhydryl groups of cell components would primarily induce an increase in the Ca2+ cytosolic concentration, followed by membrane depolarization and activation of a plasma membrane NADPH oxidase. This latter effect, producing active oxygen species, might further influence plasma membrane permeability, leading to the massive release of electrolytes from the tissue.

Pyrroloquinoline quinone: a novel vitamin?

Pyrroloquinoline quinone (PQQ), otherwise known as methoxatin, is a water-soluble, redox-cycling orthoquinone that was initially isolated from cultures of methylotropic bacteria. It has been found to be a cofactor of some bacterial alcohol dehydrogenases, and is present in many animal tissues. It may be a novel vitamin because it has been shown to be essential for normal growth and development. The redox-cycling ability of PQQ enables it to scavenge or generate superoxide. When fed to animals as a supplement, PQQ prevents oxidative changes that would ordinarily occur. It has been reported to inhibit glutamate decarboxylase activity and protect against N-methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity in the brain. It appears that in the whole animal, however, PQQ does not cross the blood-brain barrier. Furthermore, it increases nerve growth factor (NGF) synthesis in mouse astroglial cells, but has to be bound to glycine to penetrate and exert this effect in whole brain. It may therefore be regarded as a "Janus faced" molecule, with its potential for a therapeutic role in the brain still in question.

Inhibition of NADPH-cytochrome P450 reductase and glyceryl trinitrate biotransformation by diphenyleneiodonium sulfate

We reported previously that the flavoprotein inhibitor diphenyleneiodonium sulfate (DPI) irreversibly inhibited the metabolic activation of glyceryl trinitrate (GTN) in isolated aorta, possibly through inhibition of vascular NADPH-cytochrome P450 reductase (CPR). We report that the content of CPR represents 0.03 to 0.1% of aortic microsomal protein and that DPI caused a concentration- and time-dependent inhibition of purified cDNA-expressed rat liver CPR and of aortic and hepatic microsomal NADPH-cytochrome c reductase activity. Purified CPR incubated with NADPH and GTN under anaerobic, but not aerobic conditions formed the GTN metabolites glyceryl-1,3-dinitrate (1,3-GDN) and glyceryl-1,2-dinitrate (1,2-GDN). GTN biotransformation by purified CPR and by aortic and hepatic microsomes was inhibited > 90% after treatment with DPI and NADPH. DPI treatment also inhibited the production of activators of guanylyl cyclase formed by hepatic microsomes. We also tested the effect of DPI on the hemodynamic-pharmacokinetic properties of GTN in conscious rats. Pretreatment with DPI (2 mg/kg) significantly inhibited the blood pressure lowering effect of GTN and inhibited the initial appearance of 1,2-GDN (1-5 min) and the clearance of 1,3-GDN. These data suggest that the rapid initial formation of 1,2-GDN is related to mechanism-based GTN biotransformation and to enzyme systems sensitive to DPI inhibition. We conclude that vascular CPR is a site of action for the inhibition by DPI of the metabolic activation of GTN, and that vascular CPR is a novel site of GTN biotransformation that should be considered when investigating the mechanism of GTN action in vascular tissue.

Stability of recombinant yeast protoporphyrinogen oxidase: effects of diphenyl ether-type herbicides and diphenyleneiodonium

Protoporphyrinogen oxidase catalyzes the oxygen-dependent aromatization of protoporphyrinogen IX to protoporphyrin IX and is the molecular target of diphenyl ether-type herbicides. Structural features of yeast protoporphyrinogen oxidase were assessed by circular dichroism studies on the enzyme purified from E. coli cells engineered to overproduce the protein. Coexpression of the bacterial gene ArgU that encodes tRNAAGA,AGG and a low induction temperature for protein synthesis were critical for producing protoporphyrinogen oxidase as a native, active, membrane-bound flavoprotein. The secondary structure of the protoporphyrinogen oxidase was 40.0 +/- 1. 5% alpha helix, 23.5 +/- 2.5% beta sheet, 18.0 +/- 2.0% beta turn, and 18.5 +/- 2.5% random-coil. Purified protoporphyrinogen oxidase appeared to be a monomeric protein that was relatively heat-labile (Tm of 44 +/- 0.5 degreesC). Acifluorfen, a potent inhibitor that competes with the tetrapyrrole substrate, and to a lower extent FAD, the cofactor of the enzyme, protected the protein from thermal denaturation, raising the Tm to 50.5 +/- 0.5 degreesC (acifluorfen) and 46.5 +/- 0.5 degreesC (FAD). However, diphenyleneiodonium, a slow tight-binding inhibitor that competes with dioxygen, did not protect the enzyme from heat denaturation. Acifluorfen binding to the protein increased the activation energy for the denaturation from 15 to 80 kJ.mol-1. The unfolding of the protein was a two-step process, with an initial fast reversible unfolding of the native protein followed by slow aggregation of the unfolded monomers. Functional analysis indicated that heat denaturation caused a loss of enzyme activity and of the specific binding of radiolabeled inhibitor. Both processes occurred in a biphasic manner, with a transition temperature of 45 degreesC.

Arachidonic acid activates NADPH oxidase by a direct, calmodulin-regulated mechanism

In intact neutrophils, arachidonic acid rapidly and transiently activated NADPH oxidase-mediated superoxide generation. Inhibitors of protein kinases (staurosporine and H-7) failed to markedly attenuate arachidonic acid-stimulated superoxide generation. Conversely, the calmodulin antagonist W-7 blocked this arachidonic acid-stimulated response. Similarly, diphenylene iodonium potently inhibited superoxide release. These results suggest that arachidonic acid directly activates the membrane-associated NADPH oxidase and calmodulin and/or calmodulin-binding proteins are required for the assembly of the active oxidase.

Inhibition of O2-reducing activity of horseradish peroxidase by diphenyleneiodonium

Plant cells respond to pathogen attach with a burst of H2O2 secretion. The question whether this defense reaction is catalysed by a NAD(P)H oxidase similar to the NADPH oxidase of phagocytic leukocytes in mammals or by an extracellular peroxidase is presently a matter of controversial debate. The observation that H2O2 production by plant cells can be inhibited by diphenyleneiodonium (DPI), a potent inhibitor of the mammalian NADPH oxidase, has fostered the view that a mammalian-type enzyme is responsible for the H2O2 production by plant cells. Here we show that DPI inhibits the NADH-dependent H2O2 production by horseradish peroxidase in the same concentration range as previously used for the inhibition of putative NADPH oxidase activity in plants. The peroxidative activity normally used for assaying peroxidase is not affected by DPI, indicating that the inhibitor specifically interferes with a partial reaction that is exclusively involved in the O2 reducing activity of the enzyme.

A newly synthesized molecule derived from ruthenium cation, with antitumour activity, activates NADPH oxidase in human neutrophils

To determine the nature of the mechanism by which certain derived ruthenium (Ru) complexes induce regression in tumour growth, we have investigated the possibility that this mechanism was associated with an increase of superoxide anion (O2-. production by phagocytic cells, which are usually found in tumour nodes. Here we present evidence that a newly synthesized complex, Ru3+-propylene-1, 2-diaminotetra-acetic acid (Ru-PDTA), derived from Ru and the sequestering ligand (PDTA), specifically stimulates O2-. production. This increase was associated with the translocation of cytosolic factors p47(phox) and p67(phox) of NADPH oxidase to the plasma membrane. The Ru-PDTA-complex-dependent O2-. production was abrogated by staurosporine, partially inhibited by diphenylene iodonium, and it was insensitive to pertussis toxin or dibutyryl cyclic AMP pretreatment. An increase of cytosolic Ca2+ levels were also detected in neutrophils treated with the Ru-PDTA complex. Also, Ru-PDTA complex induced the phosphorylation of tyrosine residues of several proteins as assessed by Western blotting. Present data are consistent with the possibility that Ru-PDTA-dependent antitumour effects are due in part to the complex's ability to stimulate the release of toxic oxygen metabolites from phagocytic cells infiltrating tumour masses.

Kinetics of protoporphyrinogen oxidase inhibition by diphenyleneiodonium derivatives

Protoporphyrinogen oxidase, the last enzyme of the common branch of the heme and chlorophyll pathways in plants, is the molecular target of diphenyl ether-type herbicides. These compounds inhibit the enzyme competitively with respect to the tetrapyrrole substrate, protoporphyrinogen IX. We used the flavinic nature of protoporphyrinogen oxidase to investigate the reactivity of the enzyme toward the 2,2'-diphenyleneiodonium cation, a known inhibitor of several flavoproteins. Diphenyleneiodonium inhibited the membrane-bound yeast protoporphyrinogen oxidase competitively with molecular oxygen. The typical slow-binding kinetics suggested that the enzyme with a reduced flavin rapidly combined with the inhibitor to form an initial complex which then slowly isomerized to a modified enzyme-inhibitor complex (Ki = 6.75 x 10(-8) M, Ki* = 4.1 x 10(-9) M). This inhibition was strongly pH-dependent and was maximal at pH 8. Substituted diphenyleneiodoniums were synthesized and shown to be even better inhibitors than 2,2'-diphenyleneiodonium: Ki = 4.4 x 10(-8) M and Ki* = 1.3 x 10(-9) M for 4-methyl-2,2'-diphenyleneiodonium, Ki = 2.2 x 10(-8) M and Ki * = 1.1 x 10(-9) M for 6-methyl-2,2'-diphenyleneiodonium, and Ki = 6.4 x 10(-9) M and Ki* = 1.2 x 10(-1)2 M for 4-nitro-2,2'-diphenyleneiodonium. The 4-nitro-2,2'-diphenyleneiodonium was a quasi irreversible inhibitor (k5/k6 > 5000). Diphenyleneiodoniums are a new class of protoporphyrinogen oxidase inhibitors that act via a mechanism very different from that of diphenyl ether-type herbicides and appear to be promising tools for studies on the structure-function relationships of this agronomically important enzyme.

Reactive oxygen species generation by human spermatozoa is induced by exogenous NADPH and inhibited by the flavoprotein inhibitors diphenylene iodonium and quinacrine

Human spermatozoa possess a specialized capacity to generate reactive oxygen species (ROS) that is thought to be of significance in the redox regulation of sperm capacitation (De Lamirande and Gagnon, 1993; Aitken et al., 1995). However, the mechanisms by which ROS are generated by these cells are not understood. In this study we have examined the possible significance of NADPH as a substrate for ROS production by human spermatozoa. Addition of NADPH to viable populations of motile spermatozoa induced a sudden dose-dependent increase in the rate of superoxide generation via mechanisms that could not be disrupted by inhibitors of the mitochondrial electron transport chain (antimycin A, rotenone, carbonyl cyanide m-chlorophenylhydrazone [CCCP], and sodium azide), diaphorase (dicoumarol) xanthine oxidase (allopurinol), or lactic acid dehydrogenase (sodium oxamate). However, NADPH-induced ROS generation could be stimulated by permeabilization and was negatively correlated with sperm function. Both NADH and NADPH were active electron donors in this system, while NAD+ and NADP+ exhibited little activity. Stereo-specificity was evident in the response in that only the beta-isomer of NADPH supported superoxide production. The involvement of a flavoprotein in the electron transfer process was indicated by the high sensitivity of the oxidase to inhibition by diphenylene iodonium and quinacrine. These results indicate that NAD(P)H can serve as an electron donor for superoxide generation by human spermatozoa and present a simple strategy for the production of motile populations of free radical generating cells with which to study the significance of these molecules in the control of normal and pathological sperm function.