Proton release associated with respiratory burst of polymorphonuclear leukocytes

The stimulation of polymorphonuclear leukocytes (PMNs) by phorbol-12-myristate-13-acetate in the presence of sodium fluoride caused the release of protons into the reaction medium concomitant with the generation of superoxide anions. The rates of oxygen consumption and proton release due to the metabolic burst were 16.3 +/- 3.5 and 10.2 +/- 1.1 nmol/min/10(7) cells respectively. When the superoxide anions were trapped with cytochrome c, the proton release was increased (35.8 +/- 0.5 nmol/min/10(7) cells) until the cytochrome c was reduced. Since the protons released from the activated cells would be consumed by the generated superoxide anions in the extracellular medium, the net amount of the protons released was 3-4-fold greater than that observed in the absence of extracellular cytochrome c. The increased proton release may be coupled to increased cellular respiration, since the inhibition of the respiratory burst with deoxyglucose, p-chloromercuribenzoic acid or chlorpromazine decreased the proton release. Amiloride (2 mM) inhibited the proton release by up to 40%. These observations suggest that some mechanisms other than a Na+/H+ antiport and carbon dioxide diffusion could be transporting the H+ generated in the cytosol of the activated PMNs.     

Activation of the lipoxygenase pathway in the methionine enkephalin induced respiratory burst in human polymorphonuclear leukocytes

In comparative studies of f-met-Leu-Phe (FMLP) and methionine enkephalin (ME) induced polymorphonuclear leukocyte (PMNL) stimulation the following results were obtained: (i) both FMLP and ME increased the intracellular killing (IK) capability of human PMNLs probably through NADPH oxidase activation, (ii) the ME-induced respiratory burst (RB) differed from the chemotactic peptide FMLP-triggered superoxide generation because the former was not accompanied by the activation of the glutathione system and the duration of the superoxide production was prolonged. The reaction was dependent on lipoxygenation, was potentiated by indomethacin (IM) and was inhibited by nordihidro-guairetic acid (NDGA), (iii) both 14C-arachidonic acid (14C-AA) release and leukotriene B4 (LTB4) synthesis of ME-treated PMNLs were elevated as compared to those of FMLP triggered cells. Our results suggest that lipoxygenation and even an increased LTB4 synthesis are involved in the ME-induced RB of leukocytes.     

Low levels of mercury inhibit the respiratory burst in human polymorphonuclear leukocytes

The objective of this investigation was to examine the effects of low levels of Hg(II) on the respiratory burst of PMNs by monitoring O2 consumption, superoxide radical formation, and chemiluminescence. Hg(II) at concentrations of 10-100 ng/ml profoundly inhibited zymosan-stimulated human cells. This inhibition was immediate in onset and occurred with minimal loss of cell viability. Effects of Hg(II) on the PMN respiratory burst were compared with those of Sn, Pb, Se, Au, Ag and Cu. Only in the case of Ag and Cu did the inhibitory effects approach those of Hg. The results indicate that Hg(II) may serve as a specific inhibitor of components of the respiratory burst.     

Protective effect of taurine on respiratory burst activity of polymorphonuclear leukocytes in endotoxemia

Summary. The aim of this study was to evaluate the effect of endotoxin on PMN leukocyte respiratory burst activity by measuring G6PD, NADPH oxidase and XO activities in guinea pig. In addition, the possible protective role of taurine against endotoxin-mediated PMN leukocyte function was examined. All experiments were performed with four groups (control, taurine, endotoxemia, taurine plus endotoxin) of ten guinea pigs. After the endotoxin was administrated (4 mg/kg) both G6PD and NADPH oxidase activities were significantly reduced compared with the control group. NADPH oxidase activity returned to the control value and G6PD activity also increased but it did not reach the control value. However when taurine was administrated (300 mg/kg) the activity of NADPH oxidase reached the control value; furthermore, G6PD activity also increased but it could not reach to the control value. When taurine was administrated alone, no effect on these enzymes was observed. Following the endotoxin administration, the activity of XO considerably increased. When taurine was administrated together with endotoxine and alone, this activity decreased compared to control value in both conditions. These results indicate that the O₂ ^•− formation in PMN leukocytes after the endotoxin administration is ensured by the catalysis of XO due to the inhibited NADPH oxidase activity. It was observed that taurine has considerable anti-inflammatory and antioxidant effects. However, conflicting results were obtained when taurine was administrated alone or together with an oxidant agent.     

Beta-endorphin and related peptides suppress phorbol myristate acetate-induced respiratory burst in human polymorphonuclear leukocytes

In the present study, the immunomodulatory effect of beta-endorphin (beta-E) and shorter pro-opiomelanocortin (POMC) fragments was evaluated by assessing their influence on respiratory burst in human polymorphonuclear leukocytes (PMN). The effect of the peptides (10(-17)M - 10(-10)M) on phorbol myristate acetate (PMA)-stimulated production of reactive oxygen metabolites was measured in a lucigenin-enhanced chemiluminescence (CL) assay. Both POMC peptides with opiate-like activity (i.e. alpha-endorphin (alpha-E), beta-E and gamma-endorphin (gamma-E] and their non-opioid derivatives (i.e. des-TYR1-beta-endorphin (dT beta E), des-TYR1-gamma-endorphin (dT gamma E), and des-ENK-gamma-endorphin (dE gamma E] were tested. With the exception of alpha-E, PMA-stimulated respiratory burst was suppressed by all POMC fragments tested. A U-shaped dose-response relation was observed. Doses lower than 10(-17)M and higher than 10(-8)M were without effect. beta-E and dT beta E both suppressed PMA-induced oxidative burst in human PMN at physiological concentrations (10(-16)M - 10(-10)M). gamma-E and dT gamma E proved to be less potent inhibitors, reaching maximal effect at higher concentrations (10(-12)M - 10(-10)M). DE gamma E exerted an even less pronounced but still significant suppressive effect at the concentration of 10(-10)M. None of the endorphins tested was shown to affect resting oxidative metabolism in the PMN. The modulatory effects of the opioid peptides could not be blocked by the opioid antagonist naloxone (10(-8)M). These data show that fragments derived from the POMC-precursor molecule modulate the activation of PMN by suppressing PMA-stimulated oxidative metabolism and that this activity does not involve a classical opiate-like receptor.     

Differential stimulation of the respiratory burst and lysosomal enzyme secretion in human polymorphonuclear leukocytes by synthetic diacylglycerols

Binding of chemoattractants to receptors on human polymorphonuclear leukocytes (PMN) stimulates the phosphodiesteric cleavage of phosphatidylinositol 4,5-bisphosphate to produce inositol 1,4,5-trisphosphate and 1,2-diacylglycerols. To investigate the possible second messenger function of diacylglycerols in PMN activation, we tested the ability of a series of synthetic sn 1,2-diacylglycerols, known to stimulate protein kinase C in other systems, to promote superoxide anion release, oxygen consumption, lysosomal enzyme secretion, and chemotaxis. None of the diacylglycerols initiated the chemotactic migration of PMN. Several of the diacylglycerols however, were, active in stimulating superoxide anion release and lysozyme secretion, with dioctanoylglycerol (diC8) being the most potent. Unexpectedly, didecanoylglycerol (diC10) induced lysosomal enzyme secretion, but failed to stimulate superoxide production or oxygen consumption. All other biologically active diacylglycerols tested displayed similar EC50 for stimulating lysozyme secretion and superoxide production. The ability of the diacylglycerols to compete for phorbol dibutyrate (PDBu) binding in intact PMN suggested a mechanism for the divergent biological activity of diC10. Although the compounds that stimulated both superoxide production and lysosomal enzyme secretion competed for essentially all [3H]PDBu binding from its receptor, diC10, which only stimulated secretion, competed for 45% of the bound [3H]PDBu. Thus diacylglycerols can selectively activate certain functions of leukocyte chemoattractant receptor. The data suggest that a discrete pool of protein kinase C may mediate activation of the respiratory burst in PMN.     

Interaction of polymorphonuclear leukocytes and viruses in humans: adherence of polymorphonuclear leukocytes to respiratory syncytial virus-infected cells

The nature of neutrophil-respiratory syncytial virus (RSV) interaction was investigated by assessing factors that influence neutrophil adherence to RSV-infected tissue culture monolayers. The adherence of neutrophils to infected cells was directly proportional to the degree of RSV replication as evidenced by infectious virus production, cytopathological changes, or viral antigen appearance. Sixty-one percent of the neutrophils adhered to the RSV-infected cells as compared with 52.7% on noninfected monolayers (P less than 0.05). The addition of RSV-specific antibody markedly increased polymorphonuclear leukocyte adherence to 88.5% (P less than 0.001). Complement in the absence of antibody augmented polymorphonuclear leukocyte adherence, but to a lesser degree, 69.0% (P less than 0.025). Arachidonic acid metabolism appeared to play a critical role in the adherence process; thromboxane was the single most important arachidonic acid metabolite. Inhibition of thromboxane synthesis reduced antibody-dependent polymorphonuclear leukocyte adherence on RSV-infected cells to 52.3% (P less than 0.025). These observations suggest a role for neutrophils in RSV infection. It is proposed that neutrophils may participate in RSV infection at the site of viral replication through the attachment to infected cells and the subsequent release of mediators of inflammation.     

Lack of correlation between calcium mobilization and respiratory burst activation induced by chemotactic factors in rabbit polymorphonuclear leukocytes

Low concentrations of FMLP, partially purified rabbit C5a, leukotriene B4 and platelet activating factor induced a rapid rise of intracellular free Ca2+ in rabbit polymorphonuclear leukocytes. However, the four factors differed markedly in their ability to activate the respiratory burst. The peptides FMLP and C5a induced a single, strong chemiluminescence response whereas the lipids leukotriene B4 and platelet activating factor induced a markedly less intense response with a two-peak profile. Respiratory burst activation by the peptides was dependent on extracellular Ca2+ whereas the lipids required both Mg2+ and Ca2+. The results indicate that mobilization of intracellular Ca2+ is insufficient by itself to induce respiratory burst activation and that the intracellular pathways leading to activation differ depending on the nature of the stimulus.     

Differences in the respiratory burst of human polymorphonuclear leukocytes induced by virulent and avirulent Legionella pneumophila Serogroup 1

Two strains of Legionella pneumophila of different virulence were examined for their influence on the metabolic oxidative activity of human polymorphonuclear leukocytes. The leukocytes exhibited decreased rates of oxygen consumption and diminished chemiluminescence activity following phagocytosis of a virulent strain of L. pneumophila serogroup 1. In contrast, phagocytosis of its multipassaged derivative rendered avirulent, was accompanied by increased rates of both oxygen consumption and chemiluminescence activity. Although no differences were observed in oxygen uptake induced by the virulent legionellae compared to leukocytes at rest, statistically significant differences were observed in the chemiluminescence responses. These observations were not unexpected, since the luminol-enhanced chemiluminescence assay, is more sensitive than the oxygen uptake assay. In spite of decreased metabolic activity of PMN in the presence of virulent legionellae, electron microscope studies showed higher numbers of intracellular L. pneumophila than the avirulent subtype. Thus, virulent and avirulent L. pneumophila can be differentiated on the basis of oxygen consumption and chemiluminescence assays.     

ESR studies on active oxygen radicals produced in the respiratory burst of human polymorphonuclear leukocytes

The mechanism and process of production of active oxygen radicals in the respiratory burst of polymorphonuclear leukocytes (PMN) stimulated with PMA (phorbol myristate acetate) was studied in this paper. The experimental results indicate that when the PMA was dilute enough or at the beginning of stimulation even when the PMA concentration was high, the spectrum of hydroxyl radical spin adducts, DMPO-OH, was dominant in the ESR spectra. However, at the maximum level of the respiratory burst, the spectrum of superoxide anion spin adducts, DMPO-OOH, was dominant.     

Desensitization and antagonism of rat polymorphonuclear leukocytes stimulated with PAF acether

The activation of rat polymorphonuclear leukocytes (PMN) with PAF-acether (platelet-activating factor) was blocked by two antagonists: 48740 RP and BN 52021. The release of beta glucuronidase was usually better inhibited than that of lysozyme suggesting that the tested antagonists interfere rather with PAF-acether exocytosis of azurophil granules. Inhibition was relatively specific, even though a moderate effect (below 34%) upon PMN activation by the two unrelated agonist n-formyl-Methionyl-Leucyl-Phenylalanine (fMLP) and leukotriene B4 sometimes reached significance. The partial persistence of inhibition to stimulation with PAF-acether after elimination of both inhibitors suggests that they do not act at the PAF-acether receptor only. Furthermore, the observation of cross desensitization between PAF-acether and fMLP may be related to common pathways and/or metabolites, including PAF-acether itself.     

Respective roles of nitric oxide and superoxide radical in the respiratory burst activity of rat polymorphonuclear leukocytes induced by hyperthyroidism

Summary

Administration of single doses of 0.1 mg of L-3,3′,5-triiodothyronine (T₃)/kg for 3 consecutive day to fed rats elicited a marked increase both in the opsonized zymosan-induced luminal-amplified integrated chemiluminescence (ICL) of isolated polymorphonuclear leukocytes (PMN) in the absence (200%) and presence (228%) of L-arginine, and in the rate of superoxide radical (O₂^.-) production (180%). In the presence of L-arginine, the ICL was significantly increased by 57 and 17% over values observed in its absence, in PMN from control rats and T₃-treated animals, respectively, an effect that was completely abolished by Nω-nitro-L-arginine. However, the net L-arginine-dependent ICL was comparable in stimulated PMN from both experimental groups, and the respective rates of nitric oxide (NO^.) production were not significantly different, either in the absence or presence of nitro-L-arginine methyl ester. It is concluded that thyroid hormone-induced respiratory burst activity of rat PMN is not dependent on changes in NO^. synthase activity, but rather on the adaptive increase in O₂^.- generation by NADPH oxidase.     

The role of adhesive interactions and extracellular matrix fibronectin from human polymorphonuclear leukocytes in the respiratory burst

The Arg-Gly-Asp (RGD) tripeptide and ajoene were used for studying the role of adhesive receptors in the respiratory burst. Activation of the respiratory burst was examined by using luminol-dependent and lucigenin-dependent chemiluminescence. Recently, it was shown that ajoene, (E, Z)-4,5,9-trithiadodeca-1,6,11-trien-9-oxide, a substance isolated from garlic extract, inhibits the binding of fibrinogen to activated platelets by direct interaction with fibrinogen receptor (Apitz-Castro, R., Lederma, E., Escalante, J. and Jain, M.K. (1986) Biochem. Biophys. Res. Commun. 141, 145-150). Taking into consideration the structural and functional similarity of integrins, it would be reasonable to assume that ajoene as well as RGD can inhibit adhesive interactions of human neutrophils. We have shown that the effect of various activators on the respiratory burst was abolished by ajoene or RGD treatment. The inhibitory effect of RGD and ajoene was dose-dependent. The treatment of neutrophils with antiserum against human plasma fibronectin inhibited the respiratory burst in response to formyl-methionyl-leucylphenylalanine (fMLP) and phorbol 12-myristate 13-acetate (PMA). This effect is dose-dependent and reversible with the addition of fibronectin. These data indicate that the respiratory burst in human neutrophils is mediated by the integrin family of receptors and that interactions between the extracellular matrix fibronectin and cells are necessary for the respiratory burst.     

Urate attenuates oxidation of native low-density lipoprotein by hypochlorite and the subsequent lipoprotein-induced respiratory burst activities of polymorphonuclear leukocytes

Oxidation converts native low-density lipoprotein (LDL) into a signal molecule promoting inflammatory processes during atherogenesis. The exact contribution of different antioxidants in prevention of LDL oxidation is not known. Uric acid efficiently scavenges oxidants including hypochlorite. We investigated the effect of different urate concentrations (25-500 mol/l) on the oxidation of isolated native LDL by sodium hypochlorite (1000 mol/l). While relative electrophoretic mobility declined continuously with increasing urate concentrations in the oxidation medium, lipid peroxidation as measured by TBARS was blunted only at high molar urate/NaOCl ratios. By decreasing oxidative modifications, urate dose-dependently (beginning with a urate/NaOCl ratio of 1:40) diminished stimulatory effects of oxidized LDL on the respiratory burst of resting polymorphonuclear leukocytes (PMNL). Protecting effects of urate against the proinflammatory action of oxidized LDL on activated cells were evident only at a molar urate/NaOCl ratio of 1:2 suggesting different sensitivities of PMNL to LDL oxidation state in dependence on their activity state.     

Synthesis and characterization of new copper- and zinc-chloroquine complexes and their activities on respiratory burst of polymorphonuclear leukocytes

The metal-chloroquine (CQ) complexes, Cu(CQ)2Cl (1), Cu(CQ)(PPh3)(NO3) (2), [Cu(OAc)2(CQ)]2 (3) ZnCl2(CQ)(H2O)2 (4), [Zn(OAc)2(CQ)(H2O)]2 (5), were synthesized and characterized by NMR, FAB-mass, elemental analysis, and UV-Vis, EPR and IR spectroscopies. The effects of these compounds on the generation of reactive oxygen species (ROS) from human neutrophils (PMNs) were tested in the concentration range 1-100 microM and compared to that of chloroquine. The data show that the copper-chloroquine complexes 1-3 inhibit neutrophil release of ROS in PMNs activated either by a phorbol ester or by phagocytosable particles. Both effects were dose-dependent, with an IC50 of approximately 10 microM. With the same stimulants, there was only modest inhibition of ROS generation by any of the zinc-chloroquine complexes 4-5 at 10-100 microM. All complexes did not show significant in vitro toxicity as assayed by the trypan blue exclusion method. Our results reinforce previous observations that many metal derivatives of anti-inflammatory drugs affect neutrophil functions with higher potency than their parent ligands.     

Activation of polymorphonuclear neutrophils by contact with collagen I and degradation of collagen

The contact of polymorphonuclear neutrophils with type I collagen molecules triggers the production of oxygen free radicals by these cells. This activation requires two short collagenic sequences and seems to involve a beta 2 integrin on the neutrophil membrane. Oxygen free radicals are capable to degrade collagen molecules into small peptides. This interaction takes place in inflammatory phenomena.     

Regulation of oscillations in filamentous actin content in polymorphonuclear leukocytes stimulated with leukotriene B(4) and platelet-activating factor.

Stimulation of neutrophils with LTB(4) or PAF results in the production of a rapidly oscillating actin polymerization/depolymerization response. Treatment of neutrophils with inhibitors of PKC prior to stimulation with ligand resulted in a masking of the F-actin oscillations. Because myosin has been shown to be a substrate for neutrophil PKC, this protein was investigated as a potential downstream mediator of F-actin oscillations. Stimulation of neutrophils with LTB(4) resulted in myosin light chain being serine phosphorylated in a PKC-dependent manner. This phosphorylation was shown to occur in a manner that is kinetically distinct from the myosin phosphorylation induced by FMLP, a potent activator of actin polymerization that alone does not induce F-actin oscillations. Additionally, disruption of intracellular actin-myosin interactions resulted in inhibition of LTB(4)- as well as PAF-induced F-actin oscillations. These data suggest that PKC and downstream phosphorylation of myosin as well as actin-myosin interaction may play roles in mediating the production of neutrophil F-actin oscillations.