Mechanisms of regulating the respiratory burst in leukocytes

Extracellular acidic pH modulates oxygen-dependent cytotoxic responses mediated by polymorphonuclear leucocytes and monocytes

In the present study, we compared the ability of human neutrophils and monocytes to display oxygen-dependent cytotoxic responses at pH 7.4 and 6.2. Our results show that cytotoxicity induced by immune complexes (IC), zymosan, N-formyl-methionyl-leucyl-phenylalanine (FMLP) and concanavalin A (Con A) were markedly increased when they were carried out at pH 6.2 instead of pH 7.4. Cytotoxicity induced by phorbol myristate acetate (PMA), on the contrary, was significantly decreased at pH 6.2. It is noteworthy that cytotoxic responses induced by IC, zymosan and Con A were also increased when, 2 h after effector cell stimulation at pH 6.2, cytotoxicity was measured at pH 7.4. Finally, when we examined possible mechanisms involved in the augmentation of cytotoxicity, we observed that the oxidative response of IC-stimulated neutrophils, measured as chemiluminescence emission, was not increased at pH 6.2, on the contrary, it was significantly decreased. The relevance of these results is discussed.

Effect of ingested pentoxifylline on neutrophil superoxide anion production

Superoxide and other oxygen radicals produced by activated polymorphonuclear leukocytes (PMN) may be important causes of tissue damage in a number of inflammatory conditions. Therefore, a drug which suppresses PMN responses in vivo is potentially important. In vitro, pentoxifylline (PTOX) inhibits superoxide anion production when PMN are stimulated with an activated complement component (C5a Des Arg) or formyl peptides but only at concentrations not achieved in the circulation. The aim of this study was to determine whether PTOX has an effect on PMN responses in vivo. Superoxide anion production, monitored by lucigenin-enhanced chemiluminescence, was inhibited by 40.5% +/- 8.0% (n = 8, P < 0.009) for C5a Des Arg and 47.7% +/- 9.6% (n = 8, P < 0.009) for formyl-methionylleucylphenylalanine stimulation 1.5 h after ingestion of 400 mg of PTOX in a slow-release tablet, with some inhibitory effects persisting at 5 h. There was a strong correlation between reduced PMN response to activated complement and plasma concentrations of three PTOX metabolites (P < 0.05), but not with plasma concentrations of the parent drug. In vitro investigations with each of the four methylxanthines showed two of these metabolites to be most effective at reducing PMN respiratory burst activity, lactoferrin release, and the expression of CD11b and CD18 molecules. Furthermore, this in vitro inhibitory activity was achieved at concentrations of metabolites achievable in vivo. The results suggest that PTOX reduces oxygen radical production and protects against unwanted tissue damage in vivo by the action of its metabolites.

Neutrophil modulation by Actinobacillus actinomycetemcomitans. II. Phagocytosis and development of respiratory burst

Compromised neutrophil function has been found in a number of patients with localized juvenile periodontitis (LJP), although the pathogenic mechanism is unknown. Since infection with Actinobacillus actinomycetemcomitans is frequently found in patients with LJP, we have evaluated in vitro the effect of a bacterial extract of A. actinomycetemcomitans on the development of the respiratory burst by neutrophils. Pre-incubation of neutrophils with bacterial extract increased H2O2 induced by FMLP and zymosan in a dose-dependent fashion. Substitution of FMLP for bacterial extract produced similar results. Moreover, FMLP and bacterial extract had an additive effect on superoxide production following phagocytosis of zymosan. In contrast, bacterial extract significantly decreased PMA-stimulated H2O2, but pre-incubation with FMLP instead of bacterial extract failed to decrease PMA-stimulated H2O2. Bacterial extract did not change the percentage of cells activated by FMLP, opsonized zymosan, or PMA. Heat-treated bacterial extract induced effects similar to non-treated extract. Bacterial extract treated with proteinase K or phenol extraction increased FMLP or zymosan stimulated H2O2 equivalent to non-treated bacterial extract. In contrast, proteinase K or phenol extraction abolished the inhibitory effect of bacterial extract on PMA-stimulated H2O2 production. The bacterial extract component(s) that inhibits PMA-stimulated H2O2 is therefore a protein(s), resistant to 56 degrees C, and is not endotoxin. The partially activated state of PMNs exposed to A. actinomycetemcomitans extract, combined with their reduced ability to respond to a protein kinase C-dependent stimulus, may partially explain the abnormalities noted in LJP patients.

Genetic Defects of Phagocyte Nadph Oxidase Activity and Activation

NADPH oxidase is the key enzyme of the free radical-generating oxidative matabolism of phagocytes. Work from our and other's laboratories has recently established that the oxidase is not a single molecular entity, but it is a multicomponent system including a NADPH-binding protein, a flavoprotein, a b-type cytochrome and other unidentified factors. A working model of the molecular nature and of the activation mechanism of phagocyte NADPH oxidase is here proposed. This model is suitable for the study and the classification of the molecular pathology of the oxidase system. The various genetic defects of the NADPH oxidase, that are the cause of chronic granulomatous disease, (CGD) are here presented and discussed.

Activation of NADPH oxidase by purine and pyrimidine nucleotides involves G proteins and is potentiated by chemotactic peptides

Human neutrophils and HL-60 leukaemic cells possess an NADPH oxidase which catalyses superoxide (O2-) formation and is activated by the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe). In dibutyryl cyclic AMP-differentiated HL-60 cells, ATP and UTP in the presence of cytochalasin B activated O2- formation with EC50 values of 5 microM and efficacies amounting to 30% of that of fMet-Leu-Phe. The potency order of purine nucleotides in activating O2- generation was ATP = adenosine 5'-O-(3-thiotriphosphate) greater than ITP greater than dATP = ADP. Pyrimidine nucleotides activated NADPH oxidase in the potency order UTP greater than dUTP greater than CTP = TTP = UDP. Pertussis toxin completely prevented activation of NADPH oxidase by fMet-Leu-Phe and UTP, whereas the effect of ATP was only partially inhibited. ATP and UTP enhanced O2- generation induced by fMet-Leu-Phe by up to 8-fold, and primed the cells to respond to non-stimulatory concentrations of fMet-Leu-Phe. Activation of NADPH oxidase by UTP but not by ATP was inhibited by various activators of adenylate cyclase. In dimethyl sulphoxide-differentiated HL-60 cells and in human neutrophils, ATP and UTP per se did not activate NADPH oxidase, but they potentiated the effect of fMet-Leu-Phe. Our results suggest that purine and pyrimidine nucleotides act via purino- and novel pyrimidinoceptors respectively, which are coupled to guanine nucleotide-binding proteins leading to the activation of NADPH oxidase. As ATP and UTP are released from cells under physiological and pathological conditions, these nucleotides may play roles as intercellular signal molecules in the activation of O2- formation.

Cationic polyelectrolytes: potent opsonic agents which activate the respiratory burst in leukocytes

Bacteria and yeasts which are "opsonized" with cationic polyelectrolytes (poly-L-arginine, poly-L-histidine and arginine-rich histone) are avidly endocytosed by both "professional" and "non-professional" phagocytes. The cationized particles also strongly activate the respiratory burst in neutrophils and in macrophages leading to the generation of chemiluminescence, superoxide and hydrogen peroxide. On the other hand, lysine and ornithine-rich polymers are poor opsonic agents. Poly L-arginine is unique in its capacity to act synergistically with lectins, with chemotactic peptides and with cytochalasin B to generate large amounts of chemiluminescence and superoxide in human neutrophils. Unlike polyarginine, polyhistidine, in the absence of carrier particles, is one of the most potent stimulators of superoxide generations, known. Neutrophils treated with cetyltrimethylammonium bromide fail to generate superoxide, but generate strong luminol-dependent chemiluminescence which is totally inhibited by sodium azide and by thiourea. Neutrophils injured by cytolytic agents (saponin, digitonin, lysolecithin) lose their chemiluminescence and superoxide-generating capacities upon stimulation by a variety of ligands. These activities are however regained by the addition of NADPH. Lysolecithin can replace polyarginine in a "cocktail" also containing lectins and cytochalasin B, which strongly activate the respiratory burst. This suggests that polyarginine acts both as a cytolytic agent and as a ligand. Arginine and histidine-rich polyelectrolytes enhance the pathogenic effects of immune complexes in vivo (reversed Arthus phenomenon) presumably by "glueing" them to tissues. Polyhistidine complexed to catalase or to superoxide dismutase, markedly enhances their efficiency as antioxidants. On the other hand polyhistidine complexed to glucose oxidase markedly enhances injury to endothelial cells suggesting that the close association of the cationized enzyme with the plasma membrane facilitates the interaction of hydrogen peroxide with the targets. A variety of cationic agents (histone, polyarginine, polyhistidine, polymyxin B) and membrane-active agents (lysophosphatides, microbial hemolysins) act synergistically with glucose oxidase or with reagent hydrogen peroxide to kill target cells. The mechanisms by which arginine- and histidine-rich polyelectrolytes activate the respiratory burst in neutrophils might involve interaction with G-proteins, the activation of arachidonic acid metabolism and phospholipase A2, or the interaction with myeloperoxidase. Naturally-occurring cationic proteins might modulate several important functions of leukocytes and the course and outcome of the inflammatory process.

Activation of the neutrophil respiratory burst by chemoattractants: regulation of the N-formyl peptide receptor in the plasma membrane

The N-formyl peptide receptor mediates a number of host defensive responses of human neutrophils that result in chemotaxis, secretion of hydrolytic enzymes, and superoxide generation. Inappropriate activation or defective regulation of these responses can result in pathogenic states responsible for inflammatory disease. The receptor is a 50 to 70-kD, integral plasma membrane glycoprotein with intracellular and surface localization. Its abundance in the membrane is regulated by membrane flow and recycling processes. Cytoskeletal interactions are believed to control its organization in the plane of the membrane and interaction with other proteins. The receptor's most important interaction is with guanyl nucleotide binding proteins that serve as signal transduction partners ultimately leading to activation of effector responses. Because the interaction of the receptor with G proteins is necessary for transduction, control of this interaction may be at the root of understanding the molecular control of responses in these cells. This review briefly summarizes some of the molecular properties, dynamics, and interactions of this receptor system in human neutrophils and discusses how these characteristics may pertain to the activation and control of superoxide generation.

Signal transduction in cells following binding of chemoattractants to membrane receptors

Binding of chemoattractants to specific cell surface receptors on human polymorphonuclear leukocytes (PMNs) initiates a variety of biologic responses, including directed migration (chemotaxis), release of superoxide anions, and lysosomal enzyme secretion. Chemoattractant receptors belong to a large class of receptors which utilize the hydrolysis of polyphosphoinositides to initiate Ca2+ mobilization and cellular activation. Receptor occupancy leads to phospholipase C-mediated hydrolysis of polyphosphoinositol 4,5-bisphosphate (PIP2) yielding inositol 1,4,5-trisphosphate (IP3) and 1,2 sn-diacylglycerol (DAG). These products synergize to initiate cell activation via calcium mobilization (IP3) and protein kinase C activation (DAG). Pertussis toxin, which ADP-ribosylates and inactivates some GTP binding proteins (G proteins), abolishes all chemoattractant-induced responses, including Ca2+ mobilization, IP3 and DAG production, enzyme secretion, superoxide production and chemotaxis. Direct evidence for chemoattractant receptor: G protein coupling was obtained using PMN membrane preparations which contain a Ca2+-sensitive phospholipase C. Hydrolysis of polyphosphoinositides at resting intracellular Ca2+ levels (100 nm) was only observed when the membranes were stimulated with the chemoattractant N-formyl-methyl-leucyl-phenylalanine (fMet-Leu-Phe) in the presence of GTP. Myeloid cells contain two distinct pertussis toxin substrates of similar molecular weight (40 and 41 kD). The 41 kD substrate resembles Gi, whereas a 40 kD substrate is physically associated with a partially purified fMet-Leu-Phe receptor preparation and may therefore represent a novel G protein involved in chemoattractant-stimulated responses. Metabolism of 1,4,5-IP3 to inositol proceeds via two distinct pathways in PMNs: (1) degradation to 1,4-IP2 and 4-IP1 or (2) conversion to 1,3,4,5-IP4, 1,3,4-IP3, 3,4-IP2 and 3-IP1. Initial formation (0-30 s) of 1,4,5-IP3 and DAG occurs at ambient intracellular Ca2+ levels, whereas formation of 1,3,4-IP3 and a second sustained phase of DAG production (30 s-10 min) require elevated cytosolic Ca2+ influx. The later peak of DAG, which is not derived from phosphoinositides, appears to be required for stimulation of respiratory burst activity. Products formed during activation can feed back to attenuate chemoattractant receptor-mediated stimulation of phospholipase C by uncoupling receptor-G protein-phospholipase C interaction.

Coregulation of NADPH oxidase activation and phosphorylation of a 48-kD protein(s) by a cytosolic factor defective in autosomal recessive chronic granulomatous disease

The mechanisms regulating activation of the respiratory burst enzyme, NADPH oxidase, of human neutrophils (PMN) are not yet understood, but protein phosphorylation may play a role. We have utilized a defect in a cytosolic factor required for NADPH oxidase activation observed in two patients with the autosomal recessive form of chronic granulomatous disease (CGD) to examine the role of protein phosphorylation in activation of NADPH oxidase in a cell-free system. NADPH oxidase could be activated by SDS in reconstitution mixtures of cytosolic and membrane subcellular fractions from normal PMN, and SDS also enhanced phosphorylation of at least 16 cytosolic and 14 membrane-associated proteins. However, subcellular fractions from CGD PMN plus SDS expressed little NADPH oxidase activity, and phosphorylation of a 48-kD protein(s) was selectively defective. The membrane fraction from CGD cells could be activated for NADPH oxidase when mixed with normal cytosol and phosphorylation of the 48-kD protein(s) was restored. In contrast, the membrane fraction from normal cells expressed almost no NADPH oxidase activity when mixed with CGD cytosol, and phosphorylation of the 48-kD protein(s) was again markedly decreased. Protein kinase C (PKC) activity in PMN from the two patients appeared to be normal, suggesting that a deficiency of PKC is not the cause of the defective 48-kD protein phosphorylation and that the cytosolic factor is not PKC. These results demonstrate that the cytosolic factor required for activation of NADPH oxidase also regulates phosphorylation of a specific protein, or family of proteins, at 48 kD. Although the nature of this protein(s) is still unknown, it may be related to the functional and phosphorylation defects present in CGD PMN and to the activation of NADPH oxidase in the cell-free system.

Inhibition of superoxide production in human polymorphonuclear leukocytes by oral treponemal factors

The inhibition of superoxide (O2-) production by human peripheral blood polymorphonuclear leukocytes (PMNs) in the presence of oral treponemes, their cellular components, and their culture supernatants was investigated. Superoxide production was inhibited 56% by a 25-microgram/ml phenol extract of a human clinical isolate. Inhibition by culture supernatants of both the clinical isolate and a reference strain was related to the bacterial phase of growth and viability, though inhibition also persisted in the decline phase. Inhibition of superoxide production was not evident when either opsonized or nonopsonized whole spirochetes were reacted with PMNs. The suppressive activity depended, therefore, on the treponemes either being disrupted or growing and releasing the inhibitory factor into the culture medium. These results suggest that oral treponemes possess factors which interfere with the activity of PMNs and thereby alter the inflammatory process in the diseased periodontal pocket.

Influence of rosmarinic acid on opsonization and intracellular killing of Escherichia coli and Staphylococcus aureus by porcine and human polymorphonuclear leucocytes

The influence of rosmarinic acid on the function of porcine and human polymorphonuclear leucocytes was tested. Rosmarinic acid inhibited the chemiluminescence of PMNL, induced by preopsonized Zymosan or phorbol myristate acetate. The killing of Escherichia coli was inhibited by rosmarinic acid at a concentration of 2 mM, but not that of Staphylococcus aureus. The inhibition of the killing was due to an impaired opsonization, caused by an adverse influence of rosmarinic acid on complement activation. Direct effects of rosmarinic acid on the killing mechanisms of PMNL were not observed.

Poly L-histidine. A potent stimulator of superoxide generation in human blood leukocytes

Poly-L-histidine (PHSTD) of molecular weight 26,000 induced the generation of large amounts of superoxide (O2-) and hydrogen peroxide (H2O2) in human neutrophils (PMNs). Despite its low solubility at neutral pH, PHSTD was bound very rapidly to the PMN surfaces. Maximal generation of O2- took place with 4-5 X 10(-6) M of PHSTD, starting after a lag of about 25 sec and proceeding for 15-17 min at a rate of 150 nmol/10(7) PMNs/min, suggesting that this polycation is one of the most potent stimulators of O2- generation known, PHSTD was found to be non-toxic for PMNs even at millimolar concentrations. Generation of O2- by PHSTD depended on extracellular calcium; it was inhibited by calcium channel blockers and by trifluoperazine, and it triggered a sharp rise in intracellular calcium as determined by the Quin 2 fluorescence technique. The generation of both O2- and H2O2 by PHSTD was partially inhibited by cytochalasin B or (CYB, CYE). On the other hand, CYB markedly enhanced the generation of both O2- and H2O2 following stimulation of PMNs either by PHSTD, polyarginine, histone, or by antibody-opsonized group A streptococci. Electron microscopic analysis and NBT reduction tests revealed that both PHSTD and PHSTD-opsonized streptococci were avidly phagocytosed by PMNs. Since CYB totally inhibited internalization of both PHSTD and the PHSTD-opsonized streptococci, it was suggested that these agents stimulated oxygen radical generation mainly on the leukocyte surfaces. Complexes (CX) formed between PHSTD and polyanethole sulfonate (a strong polyanion) or between histone and the polyanion mimicked immune CX in their ability to trigger the generation of large amounts of O2- which were inhibited by CYB. Generation of O2- and chemiluminescence either by PHSTD or by PHSTD-opsonized streptococci were markedly inhibited by poly-L-glutamate, suggesting that PHSTD acted as a cationic agent which interacted via electrostatic forces with some negatively charged sites in the leukocyte membrane. Generation of H2O2 by PHSTD was also markedly inhibited by deoxyglucose, KCN, DASA, as well as by the lipoxygenase inhibitors nordihydroguaiaretic acid, phenidone, and propylgallate. On the other hand, cyclooxygenase inhibitors such as aspirin, indomethacin, and piroxicam were inactive, suggesting that arachidonic acid metabolism via lipoxygenase pathway might have been involved in the activation by PHSTD of the NADPH oxidase in PMNs.(ABSTRACT TRUNCATED AT 400 WORDS)

Fatty-acid-induced activation of NADPH oxidase in plasma membranes of human neutrophils depends on neutrophil cytosol and is potentiated by stable guanine nucleotides

Both cis and trans unsaturated fatty acids and sodium dodecyl sulfate activated NADPH oxidase in plasma membranes of human neutrophils in the presence of neutrophil cytosol. In contrast, 5,8,11,14-icosatetraynoic acid, saturated fatty acids, esters, peroxides and 4 beta-phorbol 12-myristate 13-acetate, a potent activator of protein kinase C, were inactive. 5,8,11,14-icosatetraynoic acid inhibited superoxide formation elicited by fatty acids. Guanosine 5'[gamma-thio]triphosphate (GTP[gamma S]), a potent activator of guanine-nucleotide-binding proteins (N-proteins) enhanced superoxide formation elicited by fatty acids up to fourfold, supporting our previous suggestion that NADPH oxidase is regulated by an N-protein [Seifert, R. et al. (1986) FEBS Lett. 205, 161-165]. Cytosols from various tissues, soybean lipoxygenase and protein kinase C, purified from chicken stomach, did not substitute neutrophil cytosol. The activity of neutrophil cytosol was destroyed by heating at 95 degrees C. Superoxide formation was not affected by the inhibitor of protein kinase C 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7). Removal of cytosolic ATP by preincubation with hexokinase and glucose, dialysis of neutrophil cytosol or chelation of calcium with EGTA did not abolish the stimulatory effect of arachidonic acid and GTP[gamma S]. Thus, the cytosolic cofactor appears to be a neutrophil-specific and heat-labile protein, which is neither a lipoxygenase nor protein kinase C.

Superoxide production by polymorphonuclear leukocytes. A cytochemical approach

Phagocytosis by polymorphonuclear leukocytes triggers a burst of oxidative metabolism resulting in hydrogen peroxide and superoxide production, and these active oxygen species function in the killing of microorganisms. A new cytochemical technique, based on a manganese dependent diaminobenzidine oxidation, has been developed to detect superoxide in these cells. It has been shown that superoxide generation is associated with the plasma membrane in cells activated by particulate (zymosan) and non-particulate (phorbol myristate acetate) stimuli. This membrane activity is maintained during invagination such that reduced oxygen is generated within the endocytic vacuoles. Reaction product is absent from unstimulated cells; additionally, formation of precipitate is blocked by omission of Mn++, low temperature, glutaraldehyde prefixation, and the presence of superoxide dismutase in the incubation medium.

Role of protein kinases in stimulation of human polymorphonuclear leukocyte oxidative metabolism by various agonists. Differential effects of a novel protein kinase inhibitor

Isoquinoline sulfonamides have recently been shown to exert novel inhibitory effects on mammalian protein kinases by competitively binding to the ATP substrate site (Hidaka, H., M. Inagaki, S. Kawamoto, and Y. Sasaki, 1984, Biochemistry, 23: 5036-5041). We synthesized a unique analog of the previously reported compounds, 1-(5-isoquinolinesulfonyl) piperazine (C-I), in order to assess the role of protein kinases in modulating the agonist-stimulated oxidative burst of human polymorphonuclear leukocytes (PMN). Compound C-I, at micromolar concentration, markedly inhibited the release of superoxide anion from human PMN stimulated with phorbol myristate acetate or the synthetic diacylglycerol, 1-oleoyl-2-acetyl glycerol. These data are consonant with previously reported data which indicate that the calcium and phospholipid-dependent protein kinase, protein kinase C, serves as the intracellular receptor for these agonists. In contrast, superoxide anion production stimulated by the complement anaphylatoxin peptide C5a or the synthetic chemotaxin formyl-methionyl-leucyl-phenylalanine were not inhibited by C-I. These data suggest that parallel pathways exist for the agonist-stimulated respiratory burst of human neutrophils, only one of which utilizes the calcium and phospholipid-dependent protein kinase.

Activation of the respiratory burst enzyme from human neutrophils in a cell-free system. Evidence for a soluble cofactor

Activation of the respiratory burst in phagocytic cells, an important host defense process, is not yet well understood. We now report the development of a cell-free system for activation of NADPH oxidase, the respiratory burst enzyme, in human neutrophils. Activation was achieved by the addition of arachidonic acid to a postnuclear supernatant (500 g) from disrupted unstimulated cells (no arachidonate, 0.2; with arachidonate, 3.4 nmol superoxide anion/min per mg) and was dependent on both the concentration of arachidonate and on the amount of cellular material present. Activity stimulated by arachidonate appeared to be NADPH oxidase based on a Michaelis constant for NADPH of 32 microM and a pH optimum of 7.0-7.5. Separation of the 500-g supernatant by high speed centrifugation revealed a requirement for both soluble and particulate cofactors. Activation of NADPH oxidase by arachidonate did not occur in the high speed pellet fraction from unstimulated cells but could be restored by the addition of the high speed supernatant. In addition, priming of intact neutrophils with low concentrations of the chemoattractant N-formyl-methionyl-leucyl-phenylalanine or the tumor promoter phorbol myristate acetate replaced the soluble factor requirement for NADPH oxidase activation by arachidonate in the high speed pellet. This cell-free system can now be used to provide further insight into the biochemical basis of priming and the terminal mechanisms involved in the activation of NADPH oxidase.