Purification and some properties of the 45 kDa diphenylene iodonium-binding flavoprotein of neutrophil NADPH oxidase

Age-related deficiencies in complex I endogenous substrate availability and reserve capacity of complex IV in cortical neuron electron transport

Respiratory enzyme complex dysfunction is mechanistically involved in mitochondrial failure leading to neurodegenerative disease, but the pathway is unclear. Here, age-related differences in mitochondrial respiration were measured in both whole and permeabilized neurons from 9-month and 24-month adult rat cortex cultured in common conditions. After permeabilization, respiration increased in both ages of neurons with excess substrates. To dissect specific deficiencies in the respiratory chain, inhibitors for each respiratory chain complex were used to isolate their contributions. Relative to neurons from 9-month rats, in neurons isolated from 24-month rats, complexes I, III, and IV were more sensitive to selective inhibition. Flux control point analysis identified complex I in neurons isolated from 24-month rats as the most sensitive to endogenous substrate availability. The greatest age-related deficit in flux capacity occurred at complex IV with a 29% decrease in neurons isolated from 24-month rats relative to those from 9-month rats. The deficits in complexes I and III may contribute to a redox shift in the quinone pool within the electron transport chain, further extending these age-related deficits. Together these changes could lead to an age-related catastrophic decline in energy production and neuronal death.

The respiratory burst oxidase

Sbarra and Karnovsky were the first to present evidence suggesting the presence in phagocytes of a special enzyme designed to generate reactive oxidants for purposes of host defense. In the years since their report appeared, a great deal has been learned about this enzyme, now known as the respiratory burst oxidase. It has been found to be a plasma membrane-bound heme- and flavin-containing enzyme, dormant in resting cells, that catalyzes the one-electron reduction of oxygen to O2- at the expense of NADPH: O2 + NADPH----O2- + NADP+ + H+ Its behavior in whole cells and its response to various activating stimuli have been described in detail, although important insights continue to emerge, as for example a very interesting new series of observations on differences in oxidase activation patterns between suspended and adherent cells. The enzyme has been shown by biochemical and genetic studies to consist of at least six components. In the resting cell, three of these components are in the cytosol and three in the plasma membrane, but when the cell passes from its resting to its activated state the cytosolic components are all transferred to the plasma membrane, presumably assembling the oxidase. Of the components initially bound to the membrane, two constitute cytochrome b558, a heme protein characteristic of the respiratory burst oxidase, and the third may represent an oxidase flavoprotein. With regard to the cytosolic components, one is a phosphoprotein and another is the NADPH-binding component, possibly a second oxidase flavoprotein. The nature of the third (p67phox) is a puzzle. Four of the six oxidase components have now been cloned and sequenced. These findings only scratch the surface, however, and many questions remain. How many oxidase components, for example, remain to be discovered, and how do they fit together to form the active enzyme? How is the route of activation of the oxidase integrated into the general signal transduction systems of the cell? How did the oxidase come to be? Could there be a widespread system that generates small amounts of O2- as an intercellular signaling molecule, as recent work is beginning to suggest, and did the ever-destructive respiratory burst oxidase arise from that innocuous system as the creation of some evolutionary Frankenstein--an oxidase from hell? Finally, will it be possible to develop drugs that specifically block the respiratory burst oxidase, and will such drugs prove to be clinically useful as anti-inflammatory agents?(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for oxidative stress in NSAID-induced colitis in IL10-/- mice

The goal of this study was to evaluate for evidence of oxidative stress in colonic inflammation in a novel model of inflammatory bowel disease, nonsteroidal anti-inflammatory drug- (NSAID-) treated interleukin-10-deficient (IL10(-/-)) mice. IL10(-/-) and wild-type (wt) mice were treated with a nonselective NSAID (piroxicam, 200 ppm in the diet) for 2 weeks to induce colitis, and parameters for oxidative stress in the colonic tissues were evaluated. Mean chemiluminescence enhanced with lucigenin in the colons from IL10(-/-) mice treated with piroxicam was more than 5-fold higher than that of the control wt group. Chemiluminescence was inhibited with diphenylethylene iodinium, but not allopurinol, indomethacin, or N-omega-nitro-L-arginine, indicating that flavin-containing enzymes were the source of the reactive oxygen species. Colonic aconitase activity in NSAID-treated IL10(-/-) mice decreased to 50% of the activity of control mice. There was no difference in the total glutathione levels in the colonic mucosa among the groups; however, glutathione disulfide levels were approximately 2-fold greater in the colon of NSAID-treated IL10(-/-) mice as compared with control groups. Immunohistochemistry studies of colons from NSAID-treated IL10(-/-) mice demonstrated intense staining with two antibodies that recognize advanced glycation endproducts formed through glycation and oxidation: anticarboxymethylysine and antipentosidine. The epithelial cells and lamina propria cells in the colons of NSAID-treated IL10(-/-) mice showed immunostaining with antinitrotyrosine, indicating the presence of reactive nitrogen species. Colonic epithelium of IL10(-/-) mice with colitis showed moderate immunostaining for 8-hydroxy-2'-deoxyguanosine in the nuclei. NSAID-treated IL10(-/-) mice treated with diphenylene idodonium chloride (DPI), an irreversible inhibitor of flavoprotein enzymes, experienced significantly reduced inflammation. Taken together, these results strongly indicate the presence of oxidative stress in the inflammatory bowel disease in NSAID-treated IL10(-/-) mice and suggests a role for oxidative stress in the pathophysiology of this model of inflammatory bowel disease.

Reaction of reduced flavins and flavoproteins with diphenyliodonium chloride

The reaction of diphenyliodonium chloride with free reduced flavins has been studied by stopped flow spectrophotometry under anaerobic conditions, and second order rate constants were determined as a function of pH. The reactive flavin species was identified as the reduced anion, based on an observed reaction pK of 6.7. The product mixture was independent of the initial concentration of reactant and contained approximately 20% oxidized flavin. The results can be modeled quantitatively on a modification of the mechanism proposed by Tew (Tew, D. G. (1993) Biochemistry 32, 10209-10215). The composition of the complex reaction mixture has been analyzed, and four flavin-phenyl adducts with distinctive absorbance and fluorescence characteristics have been identified, involving substitution at the flavin C4a, N5, and C8 positions. Inactivation of flavoprotein enzymes by diphenyliodonium has also been studied, and several examples were found where inactivation occurs readily, despite noninvolvement of radical intermediates in their reaction mechanisms. It can be concluded that inactivation by phenyliodonium species is not a valid indicator of catalytic mechanism involving radical intermediates. One of the several factors determining inactivation is maintenance of the enzyme flavin in the reduced form in the steady state of catalysis, the other factors being redox potential and accessibility of the inhibitor to the flavin active site.

Diphenyleneiodonium inhibits NF-kappaB activation and iNOS expression induced by IL-1beta: involvement of reactive oxygen species

AIMS

In this work, we studied the mechanisms by which diphenyleneiodonium chloride (DPI) inhibits nitric oxide (NO) synthesis induced by the proinflammatory cytokine interleukin-1beta (IL-1) in bovine articular chondrocytes. To achieve this, we evaluated the ability of DPI to inhibit the expression and activity of the inducible isoform of the NO synthase (iNOS) induced by IL-1. We also studied the ability of DPI to prevent IL-1-induced NF-kappaB activation and reactive oxygen species (ROS) production.

RESULTS

Northern and Western blot analysis, respectively, showed that DPI dose-dependently inhibited IL-1-induced iNOS mRNA and protein synthesis in primary cultures of bovine articular chondrocytes. DPI effectively inhibited NO production (IC50=0.03+/-0.004 microM), as evaluated by the method of Griess. Nuclear factor-kappa B (NF-kappaB) activation, as evaluated by electrophoretic mobility shift assay, was inhibited by DPI (1-10 microM) in a dose-dependent manner. IL-1-induced ROS production, as evaluated by measurement of dichlorofluorescein fluorescence, was inhibited by DPI at concentrations that also prevented NF-kappaB activation and iNOS expression.

CONCLUSIONS

DPI inhibits IL-1-induced NO production in chondrocytes by two distinct mechanisms: (i) by inhibiting NOS activity, and (ii) by preventing iNOS expression through the blockade of NF-kappaB activation. These results also support the involvement of reactive oxygen species in IL-1-induced NF-kappaB activation and expression of NF-kappaB-dependent genes, such as iNOS.

Elicitor induced defence responses in medicago sativa

•  The effects are reported here of an elicitor prepared from liquid cultures of an isolate of Verticillium albo-atrum, which is nonpathogenic to Medicago sativa, on accumulation of H₂ O₂ , medicarpin, deposition of phenolic polymer and phenylalanine ammonia-lyase (PAL) activity in cultured cells of Medicago sativa L. cv. Kabul (lucerne). •  PAL activity and phytoalexins were assayed spectrophotometically and by HPLC, respectively. The scopoletin fluorescence-quenching and thioglycolic acid methods were used to measure H₂ O₂ and phenolic polymer deposition, respectively. •  Studies with inhibitors suggested that an NAD(P)H oxidase and a peroxidase were involved in the elicitor stimulated accumulation of H₂ O₂ and that an increase in cytosolic Ca²⁺ , but not H₂ O₂ , was part of a signalling pathway leading to the induction of defence responses. •  Both the influx of Ca²⁺ and release of Ca²⁺ from intracellular stores forms part of the signalling pathway leading from perception of elicitor to induction of defence responses. Although H₂ O₂ is not part of the pathway, evidence is presented that O₂ ^- is part of the signal transduction chain.

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.

Overexpression of the FAD-binding domain of the sulphite reductase flavoprotein component from Escherichia coli and its inhibition by iodonium diphenyl chloride

SiR-FP43, the NADPH- and FAD-binding domain of the Escherichia coli sulphite reductase flavoprotein component (SiR-FP), has been overexpressed and characterized. It folds independently, retaining FAD as a cofactor and the catalytic properties associated with the presence of this cofactor. Iodonium diphenyl chloride (IDP) was shown to be a very efficient inhibitor of SiR-FP43 and SiR-FP60, the monomeric form of SiR-FP, containing both FMN and FAD as cofactors (K(i) = 18.5 +/- 5 microM, maximal inactivation rate = 0.053 +/- 0.005 s(-1)). In both cases, inactivation was shown to result from covalent binding of a phenyl group to FAD exclusively, in marked contrast with previous results obtained with cytochrome P450 reductase (CPR), where FMN and a tryptophan were phenylated, but not FAD. However, our kinetic analyses are in agreement with the inhibition mechanism demonstrated with CPR [Tew (1993) Biochemistry 32, 10209-10215]. Nine different FAD phenylated adducts were isolated and, for the first time, two FAD phenylated adducts were identified directly after extraction from a protein. Taken together, our results have shown that flavoprotein inactivation by IDP is not a reliable indicator for a flavin radical intermediate in catalysis.

Inhibition of the endothelial isoform of nitric oxide synthase impairs long-term memory formation in the chick

Previous studies with general inhibitors of nitric oxide synthase have yielded variable and contradictory results with respect to their effects on memory. This may have been due to differential effects of blocking the various isoforms of this enzyme. We show that day-old chicks trained on a single-trial passive-avoidance task suffered significant memory loss from approximately 40 min post-training following post-training intracranial administration of a potent inhibitor of eNOS. Administration of a specific nNOS or iNOS inhibitor at the same time had no effect on retention, although a role for either of these isoforms when administered at a different time after learning has yet to be fully investigated. The onset of memory loss following eNOS inhibition is the same as observed following general NOS inhibition, which suggests that amnestic effects observed in previous studies using nonspecific inhibitors may be attributable to blocking the function of eNOS. The findings indicate that eNOS may play a role in memory formation for this task, which is at least distinct from any role that may be played by nNOS.

Superoxide production from paraquat evoked by exogenous NADPH in pulmonary endothelial cells

Superoxide production from paraquat in a pulmonary microvascular endothelial cell (PMEC) suspension was demonstrated using 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-alpha]pyraz in-3-one (MCLA), a chemiluminescence probe, to detect superoxide anions. Increased rates of superoxide production from paraquat, which were sensitive to superoxide dismutase (SOD), required the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the reaction medium, and occurred instantaneously after the addition of NADPH, which is impermeable to cell membranes. NADH as an electron donor was not as effective, and xanthine or succinate had no influence. Paraquat was anaerobically reduced in the presence of NADPH and PMECs to yield a one-electron reduced radical, and the reduction was inhibited by NADP+. Diphenyleneiodonium, an inhibitor of flavoprotein reductases, also markedly inhibited both paraquat reduction and superoxide production. These results indicate that NADPH-dependent superoxide production from paraquat probably occurs by a flavoprotein with NADPH-dependent reductase activity in cell membranes. NADPH-dependent superoxide production from paraquat was also reproduced using adherent PMECs on wells. Under these conditions, superoxide production was enhanced with agonists, including interleukin-1beta, A23187, and phorbol 12-myristate 13-acetate. The effect of the former two was blocked with staurosporine, while the latter's effect was suppressed with calyculin A.

Dye-ligand and metal chelate poly(2-hydroxyethylmethacrylate) membranes for affinity separation of proteins

Cibacron Blue F3GA was covalently immobilized onto poly(2-hydroxyethyl methacrylate) pHEMA) membranes via the nucleophilic reaction between the chloride of its triazine ring and the hydroxyl group of pHEMA. Then, Fe3+ ions were complexed by chelation with the immobilized Cibacron Blue F3GA molecules. Different amounts of Fe3+ ions were loaded on the membranes by changing the concentration of Fe3+ ions and pH of the reaction medium. Membranes with or without Fe3+ were used in the adsorption of glucose oxidase, catalase and bovine serum albumin. The adsorption capacities of these membranes were determined by changing pH and the concentration of the proteins in the adsorption medium. The adsorption phenomena appeared to follow a typical Langmuir isotherm. The maximum capacities (qm) of the Fe3+ complexed membranes for glucose oxidase, catalase and bovine serum albumin (8.70 x 10(-3) mumol m-2, 2.15 x 10(-3) mumol m-2 and 2.21 x 10(-3) mumol m-2) were greater than those of the untreated membranes (6.79 x 10(-3) mumol m-2, 1.34 x 10(-3) mumol m-2 and 1.94 x 10(-3) mumol m-2) respectively. The nonspecific adsorption of the enzymes and the protein on the pHEMA membranes was negligible.

Enhanced mitochondrial radical production in patients which rheumatoid arthritis correlates with elevated levels of tumor necrosis factor alpha in plasma

Mitochondrial dysfunction contributes to cell damage in a number of human diseases. One significant mechanism by which mitochondria damage cells is by producing reactive oxygen species from the respiratory chain. In this study we measured the production of reactive oxygen species by leukocyte mitochondria in blood from rheumatoid arthritis patients. To do this we used the chemiluminescence of lucigenin, which is accumulated by mitochondria within cells and reacts with superoxide to form a chemiluminescent product. By using specific inhibitors we could distinguish between the production of reactive oxygen species by mitochondria and by NADPH oxidase. There was a five-fold increase in mitochondrial reactive oxygen species production in whole blood and monocytes from patients with rheumatoid arthritis, when compared to healthy subjects or patients with non-rheumatic diseases. There was no increases in mitochondrial reactive oxygen species production by neutrophils from rheumatoid arthritis patients. The enhanced mitochondrial radical production in rheumatoid arthritis patients correlated significantly with increased levels of tumor necrosis factor alpha in plasma (p < 0.0001). As tumor necrosis factor alpha is known to increase mitochondrial reactive oxygen species production the elevated mitochondrial radical formation seen in rheumatoid arthritis patients may be due to activation of the mitochondrial radical production. These data suggest that elevated mitochondrial oxidative stress contributes to the pathology of rheumatoid arthritis.

Antiinflammatory effects of NADPH oxidase inhibitors

Proinflammatory cytokines prime the membrane-bound NADPH oxidase of neutrophils and monocytes of mice suffering from experimental arthritis so as to attain an activated state, which, upon a second stimulus, releases 6-fold increased levels of reactive oxygen species (ROS) than do unprimed phagocytes. Enhanced NADPH oxidase activity deregulates ROS-dependent signal transduction pathways of inflammation, which play a crucial role in the pathogenesis of arthritis. The antiarthritic reactivity of two inhibitors of NADPH oxidase, diphenylene iodoniumchloride (DPI) and staurosporine, was tested in male DBA/1 x B10A(4R) hybrid mice suffering from potassium peroxochromate arthritis. Daily doses of 2.8 mumol/kg of DPI or 30 nmol/kg of staurosporine sufficed to inhibit the arthritis by 50%. A complete inhibition was obtained with 10 mumol/kg of DPI, and 100 nmol/kg of staurosporine suppressed the arthritis by 85%. The onset, progression, and remission of arthritis correlated to both the activity of phagocytic NADPH oxidase (r = 0.750) and to overt disease symptoms as judged by the arthritis index. Our data support the hypothesis that oxidative stress plays a pivotal role in the pathology of arthritis, which can be therapeutically targeted by NADPH oxidase inhibitors.

The Ca2+/NADPH-dependent H2O2 generator in thyroid plasma membrane: inhibition by diphenyleneiodonium

The thyroid plasma membrane contains a Ca(2+)-regulated NADPH-dependent H2O2-generating system which provides H2O2 for the peroxidase-catalysed biosynthesis of thyroid hormones. The electron transfer from NADPH to O2 catalysed by this system was studied by using diphenyleneiodonium (DPI), an inhibitor of flavo- and haemo-proteins. The prosthetic group of the H2O2 generator was removed by incubation with 5 mM CHAPS at 40 degrees C, and an active holoenzyme was reconstituted with FAD, but not with FMN. The H2O2-generating system also had an intrinsic Ca(2+)-dependent NADPH:ferricyanide reductase activity which is probably linked to its flavodehydrogenase component (or domain). Both activities, H2O2 production and ferricyanide reductase activity, were inhibited by DPI, with similar K1/2 (2.5 nmol/mg of protein). DPI only inhibited a system reduced with NADPH in the presence of Ca2+. NADPH could not be replaced by NADP+, NADH or sodium dithionite, suggesting the need for specific mild reduction of a redox centre in a particular conformation. Ferricyanide protected both activities against inhibition by DPI; the NADPH:ferricyanide reductase activity was completely protected at a ferricyanide concentration 20 times lower than that needed to protect the H2O2 formation, implying at least two target sites for DPI. One might be the flavodehydrogenase component; the other was beyond, on the entity which transfers the electrons to O2. This second site has not been identified.

Mechanisms for the activation/electron transfer of neutrophil NADPH-oxidase complex and molecular pathology of chronic granulomatous disease

Professional phagocytes, neutrophils, possess a unique membrane-associated NADPH-oxidase system, dormant in resting cells, which becomes activated upon exposure to the appropriate stimuli and catalyzes the one-electron reduction of molecular oxygen to superoxide, O2-. Oxidase activation involves the assembly, in the plasma membrane, of membrane-bound and cytosolic constituents of the oxidase system, which are disassembled in the resting state. The oxidase system consists of two plasma membrane-bound components; low-potential cytochrome b558, which is composed of two subunits of 22-kDa, and 91-kDa, and a possible flavoprotein related to the electron transport between NADPH and cytochrome b558. Recent reports have indicated that FAD-binding sites of the oxidase are contained in cytochrome b558. At least two cytosolic components, 67-kDa protein and a phosphorylated 47-kDa protein, are known to translocate to the plasma membrane, ensuring assembly of an active O2(-)-generating NADPH-oxidase system. It is the purpose of this review to focus on recent data concerning electron transfer mechanisms of the activated neutrophil NADPH-oxidase complex and molecular pathology of chronic granulomatous disease.

Activation factors of neutrophil NADPH oxidase complex

Professional phagocytes, neutrophils, possess a unique membrane-associated NADPH oxidase system, dormant in resting cells, which becomes activated upon exposure to the appropriate stimuli and catalyzes the one-electron reduction of molecular oxygen to superoxide, O2-. Oxidase activation involves the assembly, in the plasma membrane, of membrane-bound and cytosolic constituents of the oxidase system, which are disassembled in the resting state. The oxidase system consists of two plasma membrane-bound components; low-potential cytochrome b558, which is composed of two subunits of 22 kDa and 91 kDa, and a flavoprotein related to the electron transport between NADPH and heme-binding domains of the oxidase. Recent reports have indicated that FAD-binding sites of the oxidase are contained in cytochrome b558 (flavocytochrome b558). At least two cytosolic components, 67 kDa protein and a phosphorylated 47 kDa protein, are known to translocate to the plasma membrane, ensuring assembly of an active O2(-)-generating NADPH oxidase system. More recently, the membrane (Raps) and cytosolic (Racs) GTP-binding proteins have been established as essential to oxidase assembly. It is the purpose of this review to focus on recent data concerning the regulatory mechanisms which lead to organization and activation of the neutrophil NADPH oxidase system.

Generation of superoxide by purified and relipidated cytochrome b559 in the absence of cytosolic activators

Purified cytochrome b559 from guinea pig macrophages was relipidated with several phospholipid mixtures. Relipidated cytochrome b559 was found capable of NADPH-dependent superoxide (O2-) production in the absence of the cytosolic components of the NADPH oxidase complex. The rate of O2- generation by cytochrome b559 varied with the type of phospholipid utilized for relipidation, was absolutely dependent on exogenous FAD, and was enhanced by a critical concentration of anionic amphiphile. It is demonstrated that exogenous FAD acts by binding to cytochrome b559. These results provide firm experimental evidence for the proposal that cytochrome b559 comprises the complete electron transporting apparatus of the O2- forming NADPH oxidase and that the cytosolic components function merely as activators.

The mechanism of the production of superoxide by phagocytes

Superoxide is produced by phagocytic cells at rates sufficient to have cytocidal effects. A wide variety of receptor-dependent and -independent agonists triggers this respiratory burst, including immunoglobin aggregates, complement fragments, and leukotriene B4. Lower rates of O2-. production are triggered by addition of specific cytokines into B-lymphocytes, endothelial cells, fibroblasts, and kidney mesangial cells; low concentration of radicals may act as signals for proliferation or other changes. The NADPH oxidase of phagocytes, characterized by the presence of FAD and a low potential cytochrome b, is organized to transfer electrons electrogenically across the plasma membrane from NADPH to O2. A proton channel permits movement of compensating H+.

The inhibition of nitric oxide-mediated relaxations in rat aorta and anococcygeus muscle by diphenylene iodonium

1. The effects of diphenylene iodonium (DPI), an inhibitor of reduced nicotinamide adenine dinucleotide phosphate-dependent oxidases (which generate superoxide anions), were studied on nitric oxide (NO)-mediated responses in isolated preparations of the rat aorta and anococcygeus muscle. 2. In aortic rings, the endothelium-dependent relaxant action of acetylcholine was reduced by DPI (0.3-10 mumol/L) in a concentration-dependent manner and abolished by the NO synthase (NOS) inhibitor L-nitro-NG-arginine methylester (L-NAME; 100 mumol/L). Relaxations induced by sodium nitroprusside (SNP) or NO were not affected by DPI or L-NAME. 3. In anococcygeus muscles, DPI (0.3-10 mumol/L) as well as L-NAME (5-100 mumol/L) produced concentration-dependent reductions of relaxations produced by nitrergic nerve stimulation. Relaxations induced by NO and SNP were not affected by either DPI or L-NAME. L-Arginine (1 mmol/L) prevented the reduction of nitrergic relaxations by L-NAME but not by DPI. 4. Contractions of anococcygeus muscles elicited by exogenous noradrenaline (1 mumol/L) were not affected or were inhibited by DPI (0.3-10 mumol/L), but the contractions elicited by noradrenergic nerve stimulation were significantly enhanced by DPI and L-NAME. When noradrenergic contractions had already been maximally enhanced by L-NAME (100 mumol/L), DPI produced no further enhancement. L-Arginine (1 mmol/L) prevented the enhancement of noradrenergic contractions by L-NAME but not by DPI. 5. The efflux of radioactivity induced by field stimulation from anococcygeus muscles previously incubated with [3H]-noradrenaline was not affected by either DPI or L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)

The respiratory burst oxidase and the molecular genetics of chronic granulomatous disease

The phagocyte respiratory burst oxidase plays a central role in the inflammatory response. This membrane-bound enzyme complex is comprised of both integral membrane and cytosolic proteins and catalyzes the formation of large quantities of superoxide in response to inflammatory stimuli. While superoxide and its oxidant derivatives normally serve a microbicidal function, excessive or inappropriate release of these products contribute to inflammatory tissue injury. Chronic granulomatous disease (CGD) is a group of inherited disorders characterized by an absent neutrophil respiratory burst, which leads to recurrent and often life-threatening infections in affected patients. The analysis of the specific cellular defects in CGD has been instrumental in the identification and characterization of individual oxidase components. Four distinct genetic subgroups are presently recognized, each involving a different protein essential for respiratory burst oxidase function. This article summarizes recent advances in the characterization of the protein components and cellular biochemistry of the respiratory burst oxidase and reviews the classification and molecular genetics of CGD. The application of these findings to new approaches to the diagnosis and treatment of CGD are also reviewed.

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

Diphenylene iodonium (Ph2I), a lipophilic reagent, is an efficient inhibitor of the production of O2- by the activated NADPH oxidase of bovine neutrophils. In a cell-free system of NADPH oxidase activation consisting of neutrophil membranes and cytosol from resting cells, supplemented with guanosine 5'-[gamma-thio]triphosphate, MgCl2 and arachidonic acid, or in membranes isolated from neutrophils activated by 4 beta-phorbol 12-myristate 13-acetate, addition of a reducing agent, e.g. NADPH or sodium dithionite, markedly enhanced inhibition of the NADPH oxidase by Ph2I. The membrane fraction was found to contain the Ph2I-sensitive component(s). In the presence of a concentration of Ph2I sufficient to fully inhibit O2- production (around 10 nmol/mg membrane protein), addition of catalytic amounts of the redox mediator dichloroindophenol (Cl2Ind) resulted in a by-pass of the electron flow to cytochrome c, the rate of which was about half of that determined in non-inhibited oxidase. A marked increase in the efficiency of this by-pass was achieved by addition of sodium deoxycholate. The Cl2-Ind-mediated cytochrome c reduction was negligible in membranes isolated from resting neutrophils. At a higher concentration of Ph2I (100 nmol/mg membrane protein), the Cl2Ind-mediated cytochrome c reductase activity was only half inhibited, which indicated that, in the NADPH oxidase complex, there are at least two Ph2I sensitive components, differing by their sensitivity to the inhibitor. At low concentrations of Ph2I (less than 10 nmol/mg protein), the spectrum of reduced cytochrome b558 in isolated neutrophil membranes was modified, suggesting that the component sensitive to low concentrations of Ph2I is the heme binding component of cytochrome b558. Higher concentrations of Ph2I were found to inhibit the isolated NADPH dehydrogenase component of the oxidase complex. A number of membrane and cytosolic proteins were labeled by [125I]Ph2I. However, the radiolabeling of a membrane-bound 24-kDa protein, which might be the small subunit of cytochrome b558, responded more specifically to the conditions of activation and reduction which are required for inhibition of O2- production by Ph2I. The O2(-)-generating form of xanthine oxidase was also inhibited by Ph2I. Inhibition of xanthine oxidase, a non-heme iron flavoprotein, by Ph2I had a number of features in common with that of the neutrophil NADPH oxidase, namely the requirement of reducing conditions for inhibition of O2- production by Ph2I and the induction of a by-pass of electron flow to cytochrome c by Cl2Ind in the inhibited enzyme, suggesting some similarity in the molecular organization of the two enzymes.

Reconstitution and characterization of the human neutrophil respiratory burst oxidase using recombinant p47-phox, p67-phox and plasma membrane

Human neutrophil respiratory burst oxidase (NADPH-oxidase) activity can be reconstituted in a cell-free system consisting of plasma membrane, cytosol and an anionic amphiphile [e.g., sodium dodecyl sulfate (SDS) or arachidonate]. Herein, we report reconstitution of oxidase activity using isolated neutrophil plasma membrane together with purified recombinant p47-phox and p67-phox which had been produced using a baculovirus expression system. Activity required an anionic amphiphile (SDS or arachidonate) and was potentiated by diacylglycerol and GTP gamma S. Serial washes of the plasma membrane failed to affect its ability to reconstitute activity, indicating that a dissociable membrane component was not present. The Km for NADPH, 43 microM, was the same as that determined using cytosol in place of recombinant factors. The EC50 values for p47-phox and p67-phox under optimal activation conditions were 220 nM and 80 nM, respectively, indicating a relatively high affinity of these components in an activation complex. Since neither cytosolic component contains a nucleotide binding consensus sequence, these data indicate that the NADPH binding component of the oxidase resides in the plasma membrane.

Determination of flavin contents in neutrophils by a sensitive chemiluminescence assay: evidence for no translocation of flavoproteins from the cytosol to the membrane upon cell stimulation

A sensitive and specific chemiluminescence (CL) method with bacterial luciferase was adapted for accurate measurement of the flavins FAD and FMN in the membrane and cytosolic fractions of neutrophils prepared from pig and human blood. The FAD and FMN contents (FAD/FMN = 100:2) in the membranes were essentially the same in resting (R) and myristate-stimulated (S) cells, although O2(-)-generation was markedly enhanced exclusively in S membranes. The O2(-)-forming activity of S samples remained unchanged or even increased after washing the membranes with buffer, although one-third of the FAD was lost during washing (a decrease from 140 to 95 pmol/10(8) cell-equivalent (CE) during washing). The cytosol is known to contain at least three components that are essential for O2- production (p47-phox, p67-phox, and a G-protein), and that are translocated to membranes upon activation, but its flavin content was one tenth of that of the membranes. The cytosol was treated with fatty acids in the absence of membranes to induce substantial precipitation of p47-phox, p67-phox and a protein of 32 kDa. No difference relative to a solvent-control was noted in the low flavin content of the precipitate indicating that these cytosolic components are not flavoproteins. These results do not support the possibility of translocation of a cytosolic flavoprotein to the membrane upon activation of the respiratory burst.

Cytochrome b-245 is a flavocytochrome containing FAD and the NADPH-binding site of the microbicidal oxidase of phagocytes

The NADPH oxidase of phagocytic cells is important for the efficient killing and digestion of ingested microbes. A very unusual low-potential cytochrome b (b-245) is the only redox molecule to have been identified in this system. The FAD-containing flavoprotein that binds NADPH and transfers electrons to the cytochrome has eluded identification for three decades. We show here that the haem/FAD ratio in the membranes does not change significantly on activation of this oxidase, indicating that the FAD is present in the membranes from the outset and not recruited from the cytosol. The FAD content of membranes from cells of patients with X-linked chronic granulomatous disease (CGD) lacking the cytochrome b was roughly one-quarter of that in normal subjects and in autosomal recessive CGD patients lacking the cytosolic protein p47-phox. Similar low amounts of FAD were present in uninduced promyelocytic (HL60) cells, suggesting that the low amount of FAD in cells from X-CGD patients was probably unrelated to this oxidase system. Cytochrome b-245 appears to bind both the haem and FAD, in a molar ratio of 2:1. The e.p.r. signal of the purified cytochrome was weak and had an asymmetric g(z) peak at g = 3.31. The purified cytochrome could be partially reflavinated (about 20%) in the presence of lipid. Amino acid sequence homology was detected between the beta-subunit of this cytochrome b and the ferredoxin-NADP+ reductase (FNR) family of reductases in the putative NADPH- and FAD-binding sites. 32P-labelled 2-azido-NADP was used as a photoaffinity label for the NADPH-binding site. Labelling that was competed off with NADP was observed in the region of the beta-subunit of the cytochrome. No labelling was seen in this region in X-CGD in three subjects in whom this cytochrome was missing and in a third in whom it was present but bore a Pro-His transposition in the putative NADPH-binding site. These studies indicate that cytochrome b-245 is a flavocytochrome, the first described in higher eukaryotic cells, bearing the complete electron-transporting apparatus of the NADPH oxidase.

Cytochrome b558: the flavin-binding component of the phagocyte NADPH oxidase

The phagocyte respiratory burst oxidase is a flavin-adenine dinucleotide (FAD)-dependent dehydrogenase and an electron transferase that reduces molecular oxygen to superoxide anion, a precursor of microbicidal oxidants. Several proteins required for assembly of the oxidase have been characterized, but the identity of its flavin-binding component has been unclear. Oxidase activity was reconstituted in vitro with only the purified oxidase proteins p47phox, p67phox, Rac-related guanine nucleotide (GTP)-binding proteins, and membrane-bound cytochrome b558. The reconstituted oxidase required added FAD, and FAD binding was localized to cytochrome b558. Alignment of the amino acid sequence of the beta subunit of cytochrome b558 (gp91phox) with other flavoproteins revealed similarities to the nicotinamide adenine dinucleotide phosphate (reduced) (NADPH)-binding domains. Thus flavocytochrome b558 is the only obligate electron transporting component of the NADPH oxidase.

Inactivation of NADPH oxidase from human neutrophils by affinity labeling with pyridoxal 5'-diphospho-5'-adenosine

When a particulate NADPH oxidase prepared from phorbol ester-activated human neutrophils was treated with pyridoxal 5'-diphospho-5'-adenosine (PLP-AMP), the superoxide anion-producing activity was inhibited according to affinity labeling kinetics. NADPH afforded a protection against inactivation which was competitive with respect to PLP-AMP; 2',5'-ADP and 2'-phospho-5' diphosphoadenosine (ATP ribose) appeared to be as potent as NADPH as protecting agents. NADP+ and ATP were less effective, while ADP and GTP-gamma-S did not protect significantly. These results suggest that PLP-AMP can be used, in conjunction with tritiated cyanoborohydride, to identify the elusive NADPH-dependent flavoprotein which is part of the electron transfer chain of NADPH oxidase.

Activation of O2(-)-generating oxidase in an heterologous cell-free system derived from Epstein-Barr-virus-transformed human B lymphocytes and bovine neutrophils. Application to the study of defects in cytosolic factors in chronic granulomatous disease

Epstein-Barr-virus-transformed human B lymphocytes (EBV B lymphocytes) stimulated by 4 beta-phorbol 12-myristate 13-acetate exhibit an NADPH-dependent oxidase activity capable of generating the superoxide anion O2-, similar to, but less efficient than that of activated neutrophils. A cell-free system of oxidase activation consisting of a membrane fraction and cytosol from EBV B lymphocyte homogenate supplemented with guanosine 5'-[gamma-thio]triphosphate (GTP[S]), arachidonic acid and Mg2+ was found to be competent in the production of O2-, assessed by the superoxide-dismutase-sensitive reduction of cytochrome c in the presence of NADPH. However, cytochrome c reduction was slow and largely insensitive both to superoxide dismutase, and to iodonium biphenyl, a powerful inhibitor of the oxidase activity in neutrophils. A markedly faster reduction of cytochrome c in the presence of NADPH was obtained with a heterologous system consisting of cytosol from EBV B lymphocytes and bovine neutrophil membranes, GTP[S], arachidonic acid and Mg2+; in this system, reduction of cytochrome c was totally inhibited by superoxide dismutase and iodonium biphenyl. These results show that EBV B lymphocytes contain a substantial amount of cytosolic factors of oxidase activation, and that the limiting factors for O2- production in B lymphocytes are the membrane components of the oxidase complex. The heterologous system of EBV B lymphocyte cytosol and bovine neutrophil membranes provided a rapid and convenient method to diagnose cytosolic defects in autosomal forms of chronic granulomatous disease. In addition, it might be a useful tool to explore the mechanism of action of the cytosolic factors in oxidase activation.

Chemiosmotic systems in medicine

The concept of chemiosmotic systems arises from the pioneering work of Peter Mitchell on two fronts. One is concerned with the mechanisms by which molecules are transported across membranes which are generally barriers to such transport. These mechanisms are inevitably molecular, and are now yielding their secrets to a combination of structural protein chemistry and molecular biology. The other front is more physiological, and explores the functional relationships between metabolism and transport. Nevertheless, the two fronts form a continuum of mutually related structure and function. Chemiosmotic systems provide a hierarchy of complexity, starting from say a uniporter reconstituted in a chemically defined bilayer, and proceeding to greater complexity in mitochondria, chloroplasts, eukaryotic and prokaryotic cell membranes, and multicellular systems. Their relationship to medicine is profound, because they provide many opportunities for therapeutic intervention. In this paper I present an overview of chemiosmotic systems at different levels of complexity, both molecular and biological, of their involvements in pathology, and of possible pharmacological treatment or prevention of disease.

The superoxide-generating oxidase of phagocytic cells. Physiological, molecular and pathological aspects

Professional phagocytes (neutrophils, eosinophils, monocytes and macrophages) possess an enzymatic complex, the NADPH oxidase, which is able to catalyze the one-electron reduction of molecular oxygen to superoxide, O2-. The NADPH oxidase is dormant in non-activated phagocytes. It is suddenly activated upon exposure of phagocytes to the appropriate stimuli and thereby contributes to the microbicidal activity of these cells. Oxidase activation in phagocytes involves the assembly, in the plasma membrane, of membrane-bound and cytosolic components of the oxidase complex, which were diassembled in the resting state. One of the membrane-bound components in resting phagocytes has been identified as a low-potential b-type cytochrome, a heterodimer composed of two subunits of 22-kDa and 91-kDa. The link between NADPH and cytochrome b is probably a flavoprotein whose subcellular localization in resting phagocytes remains to be determined. Genetic defects in the cytochrome b subunits and in the cytosolic factors have been shown to be the molecular basis of chronic granulomatous disease, a group of inherited disorders in the host defense, characterized by severe, recurrent bacterial and fungal infections in which phagocytic cells fail to generate O2- upon stimulation. The present review is focused on recent data concerning the signaling pathway which leads to oxidase activation, including specific receptors, the production of second messengers, the organization of the oxidase complex and the molecular defects responsible for granulomatous disease.

Diphenylene iodonium, an inhibitor of free radical formation, inhibits platelet aggregation

Diphenylene iodonium is an inhibitor of the enzyme NADPH-oxidase and prevents the generation of oxygen-derived free radicals in neutrophils (Cross and Jones, 1986). Here we show that diphenylene iodonium (0.25-2 microM) inhibited, according to the dose, thrombin-induced platelet-aggregation in human washed platelets and ADP-induced platelet aggregation in platelet-rich plasma. At the concentrations which inhibited platelet aggregation diphenylene iodonium did not alter platelet concentrations of cAMP or cGMP but enhanced the anti-platelet activity of iloprost, sodium nitroprusside or cultured endothelial cells. These findings highlight the importance of free radicals as platelet pro-aggregatory agents.

Respiratory burst oxidase and three of four oxidase-related polypeptides are associated with the cytoskeleton of human neutrophils

Resting and phorbol-activated human neutrophils were separated by treatment with Triton X-100 into detergent-extractable and cytoskeleton fractions. Respiratory burst oxidase activity was restricted entirely to the cytoskeleton. The cytoskeleton also contained approximately 15% of the neutrophil cytochrome b558, an oxidase-associated heme protein, as well as most of the oxidase-related cytosolic polypeptide p67phox. In contrast, the components of the oxidase-associated phosphoprotein family p47phox were found almost exclusively in the detergent extract, suggesting that p47phox is needed for oxidase activation but not for O2- production by the activated oxidase. Activation of the oxidase had no apparent effect on the distribution of any of these species between the cytoskeleton and the detergent extract. Our results support earlier studies implying that the cytoskeleton participates in an important way in regulating the activity of the O2(-)-forming respiratory burst oxidase of neutrophils.

Inhibition of O2-. generating oxidase of neutrophils by iodonium biphenyl in a cell free system: effect of the redox state of the oxidase complex

The conditions of inhibition of neutrophil O2-. generating oxidase by iodonium biphenyl (IBP) were studied. In a cell free system of oxidase activation consisting of neutrophil membranes and cytosol, GTP-gamma-S, Mg2+ and arachidonic acid, the inhibitory effect of IBP depended on the redox conditions of the medium. Inhibition was observed when the medium was supplemented with dithionite or NADPH. When the cell free system was incubated with IBP in the absence of reducing agents, full oxidase activity was recovered after removal of free IBP by gel filtration. Bovine neutrophil membranes, but not cytosol, contained component(s) sensitive to IBP. Upon treatment of neutrophil membranes by IBP followed by reduction, the spectrum of reduced cytochrome b558 was modified, suggesting that cytochrome b558 is a target site for IBP.

The use of diphenylene iodonium and its analogues to investigate the role of the NADPH oxidase in the tumoricidal activity of macrophages in vitro

Lipopolysaccharide (LPS) was shown to induce tumoricidal activity in peritoneal macrophages. The optimal concentration was found to be 25 micrograms/mL. Approximately 20-h exposure to LPS was required before maximal tumor cell killing was attained. Optimal tumor killing was obtained with a ratio of tumor cell to macrophages of 1:40 with the macrophages in a confluent layer. Diphenylene iodonium (DPI) reduced the tumor cell killing in a dose dependent manner up to 1 microM. Under similar conditions DPI was shown to inhibit the superoxide production of macrophages and this supports the view that the production of oxygen radicals is important in the killing of tumor cells by macrophages and that the inhibitor DPI can be used to investigate their contribution to cytotoxicity.

Inhibition by aminoacyl-chloromethane protease inhibitors of superoxide anion production by phorbol-ester-stimulated human neutrophils. The labeled target is a membrane protein

In a previous paper, we described the kinetic characteristics of the inhibition exerted by the protease inhibitors tosylphenylalanyl and tosyllysyl chloromethanes on superoxide production by human polymorphonuclear leukocytes when stimulated by phorbol esters [E. C. Conseiller & F. Lederer (1989) Eur. J. Biochem. 183, 107-114]. The results suggested the existence of a specific target which was affinity labeled by the inhibitors. The target appeared to be neither a protease, nor intracellular enzymes which can be inhibited in vitro by the chloromethanes (protein kinase C, hexokinase and enzymes of the hexose monophosphate shunt). In the present work, using the cell-free reconstitution assay for superoxide production, we substantiate the hypothesis that the chloromethanes, target is on the plasma membrane. We have radiolabeled the membranes of cells inactivated before or after phorbol ester stimulation, using either [3H]KBH4 reduction after reaction with unlabeled inactivator, or tritiated tosylphenylalanyl chloromethane. In all cases, besides a certain background of non-specific labeling, a radioactive band of Mr 15,000 can be observed upon SDS/PAGE of radiolabeled membranes. We suggest that it is the chemical modification of this protein which is responsible for inactivation of superoxide production. Its identity and its role in the oxidative burst remain to be determined.

Superoxide generation by EBV-transformed B lymphocytes. Activation by IL-1 beta, TNF-alpha and receptor independent stimuli

The generation of superoxide by Epstein-Barr virus (EBV)-transformed human B lymphocytes can be stimulated by a range of compounds; receptor-dependent stimuli include tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and lipopolysaccharides (LPS), and independent stimuli include AlF3, A21387 and ionomycin. The stimuli suggest that the activation pathway for the lymphocyte oxidase is similar to that proposed for the neutrophil oxidase. Although the rate of superoxide production was lower than that by neutrophils, the respiratory burst was much prolonged. It is possible that this superoxide generation by lymphocytes may have a biological function.