Role of myeloperoxidase in the respiratory burst of human neutrophils

Myeloperoxidase (MPO), a heme enzyme present in the primary granules of polymorphonuclear leukocytes (PMNs), has been demonstrated to participate in the oxygen-dependent microbicidal activity of these cells. Evidence for the importance of MPO in this role comes in part from studies of normal PMNs treated with the heme enzyme inhibitor, sodium azide. MPO has also been suggested to regulate the respiratory activity of PMNs during phagocytosis. The role of MPO in PMN oxygen metabolism was examined by studying parameters of the respiratory burst of PMNs from a number of unrelated MPO-deficient subjects; in addition, the ability of heme enzyme inhibitors to duplicate the MPO-deficient state was studied by treating normal and MPO-deficient cells with these compounds. MPO-deficient PMNs were found to have a time-dependent hypermetabolic response as assessed by measurement of oxygen consumption, superoxide generation, hydrogen peroxide release, and hexose monophosphate shunt activity. Catabolic pathways for hydrogen peroxide were normal, suggesting the increased recovery of oxygen metabolites reflects increased production rather than decreased catabolism of H2O2. These observations support the concept that MPO may play an important role in terminating the respiratory burst of normal PMNs. The three heme enzyme inhibitors studied--sodium azide, potassium cyanide, and 3-aminotriazole--differed greatly in the degree to which they inhibited various enzymatic systems in the PMN. Nonetheless, as a group, they exerted qualitatively similar effects on oxygen metabolism of normal and of MPO-deficient PMNs. This indicates that many of the mechanisms by which heme enzyme inhibitors influence PMN metabolism are independent of the inhibition of MPO. Conclusions from studies using such treatment of PMNs should be interpreted with caution.     

Stimulation of the respiratory burst in human neutrophils by crystal phagocytosis

Exposure to monosodium urate crystals (MSU) stimulated the respiratory burst of human neutrophils as measured by increased O2 consumption and the generation of superoxide radicals (O(2)). From the comparison of data derived from nitroblue tetrazolium and cytochrome C reduction (two methods of detecting O(2) release), it appears tht O(2) production in response to MSU may be compartmentalized, i.e., occur predominantly in the intracellular space. After exposure to MSU, neutrophils from patients with chronic granulomatous disease lost viability at the normal rate; thus products of the respiratory burst are not likely to be responsible for cell death.     

Effects of oxygen tension and pH on the respiratory burst of human neutrophils.

The respiratory burst of human neutrophils was measured under conditions of hypoxia and low pH. O2 -- production by neutrophils activated with opsonized zymosan fell slowly as the oxygen concentration declined to 1%, then dropped more sharply, reaching negligible levels at oxygen concentrations less than 0.25%. Production was half maximal at an oxygen concentration of 0.35% (equivalent to approximately 10-microM dissolved oxygen). O2- production by the cell-free O2- -forming system prepared from zymosan-activated neutrophils showed a similar dependence on oxygen concentration. A drop in pH caused decreases in both oxygen consumption and O2-- production by zymosan-treated neutrophils, values at PH 6.0 being 10%--20% of those observed at pH 7.5. Experiments with the cell-free O2-- -forming system suggested that this decline in respiratory burst activity at low pH was due to inefficient activation of the O2-- -forming enzyme under acidic conditions.     

Proton channels,plasma membrane potential,and respiratory burst in human neutrophils

Abstract: When confronted with invading microorganisms, neutrophils undergo a number of nearly synchronous reactions including the generation of microbicidal reactive oxygen intermediates by the NADPH oxidase. These reactions are accompanied by a slow depolarization, from resting values of – 60 mV to levels probably exceeding 0 mV. The depolarization is transient, indicating that a compensatory charge transport mechanism is activated. Activation of the oxidase system causes a massive burst of metabolic acid generation that would, if uncompensated, lower the intracellular pH of neutrophils by over 5 units, to lethal levels (pH = 2). Neutrophils must therefore possess particularly effective regulatory systems to avoid excessive cytosolic acidification. The recently described H ⁺ conductance of neutrophils may counteract both the acidification and the depolarization. Activation of the H ⁺ conductance occurs at depolarizing voltages and is promoted by cytosolic acidification, a combination that takes place during the respiratory burst. The NADPH oxidase of neutrophils is thus associated to an unusual, particularly efficient mechanism of H ⁺ export and charge compensation. The sequential activation of these two systems causes neutrophils to depolarize through the activation of an electron transport chain, and to repolarize through the activation of a H ⁺ conductance.     

Sickle erythrocytes adhere to polymorphonuclear neutrophils and activate the neutrophil respiratory burst

The vasoocclusive process in patients with sickle cell disease (SCD) is complex and involves interactions among sickle erythrocytes (SS-RBC), vascular endothelium, and plasma and cellular components. The role of neutrophils (PMN) in vasoocclusion has not been examined. Patients with SCD appear to have chronically activated PMN. Because the first step in PMN activation is particle recognition, we explored whether normal PMN recognize SS-RBC and whether this recognition results in PMN monolayers, significantly more SS-RBC adhered to the PMN than did normal erythrocytes (AA-RBC; P < .001). Preincubation of erythrocytes with autologous plasma significantly increased the adherence of SS-RBC to PMN but had no effect on AA-RBC (P < .001). When adhesion of density fractionated SS-RBC was performed, dense SS-RBC showed greater adherence to the PMN monolayers than did light SS-RBC (P < .001). To determine mechanisms of this adhesion, IgG and Arg-Gly-Asp-Ser (RGDS) receptor sites on PMN were saturated. IgG inhibited adherence of dense SS-RBC, whereas RGDS inhibited adherence in both fractions, although to a greater extent in the light fraction. We measured SS-RBC activation of PMN by incubating SS-RBC with 2', 7'-Dichloro-fluroescin Diacetate (DCF)-labeled PMN. Incubation of PMN with SS-RBC resulted in a significant increase in fluorescence compared to AA-RBC. We show here that PMN recognize SS-RBC through multiple mechanisms and that this recognition results in activation of PMN. These findings contribute to the understanding of vasoocclusive crisis in patients with SCD and may have therapeutic implications.     

Basic fibroblast growth factor modulates the surface expression of effector cell molecules and primes respiratory burst activity in human neutrophils

Basic fibroblast growth factor (b-FGF) mediates a variety of biological responses such as angiogenesis and hematopoiesis. We examined the effect of b-FGF on human neutrophil functions in vitro. The surface expression of effector cell molecules on neutrophils was determined by flow cytometry and monoclonal antibodies. b-FGF increased the expression of CD11b leukocyte integrin and complement receptor type 1 on neutrophils and decreased the expression of L-selectin on neutrophils in a dose- and time-dependent manner. We also examined the effect of b-FGF on the respiratory burst activity in neutrophils. Although b-FGF alone did not induce intracellular oxidative product formation by neutrophils, it enhanced H(2)O(2) production in neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine or phorbol myristate acetate. These findings suggest that b-FGF may participate in the inflammatory process via modulating the surface expression of effector cell molecules and enhancing respiratory burst activity in neutrophils.     

Inhibition of respiratory burst activity in alveolar macrophages by bisbenzylisoquinoline alkaloids: characterization of drug-cell interaction.

The objective of this study was to investigate the effects of various bisbenzylisoquinoline (BBIQ) alkaloids on respiratory burst activity of alveolar macrophages and to characterize the interaction of these drugs with alveolar phagocytes. BBIQ alkaloids were chosen for study because they exhibit a wide range of antifibrotic potencies in a rat model, with tetrandrine being very effective and tubocurarine being ineffective. These drugs inhibited zymosan-stimulated oxygen consumption with a potency sequence of tetrandrine (TT) approximately fangchinoline (FA) > berbamine (BE) approximately cepharanthine (CE) approximately cycleanine (CY) > tubocurarine (TU). This inhibition of respiratory burst activity could not be attributed to a drug-induced decline in the ATP content of these pneumocytes. Drug binding to alveolar macrophages was directly dependent on temperature and drug concentration. The sequence for binding capacity was FA > TT approximately BE approximately CY > CE > TU. Therefore, there was no simple relationship between binding capacity and inhibitory potency. Binding capacity was not related to lipophilicity of these alkaloids. In addition, tetrandrine failed to bind to metabolically dead cells or sonicated macrophage preparations. These data suggest that the interaction of BBIQ alkaloids with phagocytes is not simply nonspecific binding to membrane lipids. Alteration of the cytoskeletal system with vinblastine, taxol, or cytochalasin B decreased tetrandrine binding by approximately 33% when added separately and by 93% when added jointly. Pre-exposure of alveolar macrophages to stimulants increased the ability of BBIQ alkaloids to inhibit both oxygen consumption and superoxide release. These data suggest that the mechanism by which BBIQ alkaloids inhibit activation of phagocytes involves microtubules and bules and microfilaments. Pre-exposure of macrophages to stimulants would change the conformation of cytoskeletal components and may make these structures more susceptible to drug interaction.     

Exposure of human neutrophils to oxygen radicals causes loss of deformability,lipid peroxidation,protein degradation,respiratory burst activation and loss of migration

The effects of oxygen radical generating system of H(2)O(2) on neutrophil deformability, lipid peroxidation, protein degradation, chemotaxis, random migration and activation were studied in the presence and absence of selected anti-oxidants such as vitamin E and carbon monoxide. Hydrogen peroxide caused a significant loss of neutrophil deformability (measured as an index of filtration), loss of chemotaxis (using chemoattractant) and loss of random migration (spontaneous migration) under agarose gel. Hydrogen peroxide also caused a significant increase in lipid peroxidation (measured as malonyldialdehye) and protein degradation (measured as free alanine). Hydrogen peroxide also caused activation of neutrophils (measured by nitroblue tetrazolium dye test). Pre-incubation of neutrophils with vitamin E prevented significantly the increase in lipid peroxidation without affecting the loss of neutrophil deformability. However, pre-incubation with carbon monoxide prevented significantly the increase in protein degradation and the loss of neutrophil deformability. The results indicate the importance of oxidatively damaged cell proteins in compromising the rheologic behaviour and migration of neutrophils, particularly under oxidative stress conditions.     

Correlations between the intensity of fMLP-dependent respiratory burst and cellular fatty acid composition in human neutrophils

Summary. The peripheral blood neutrophils were isolated from a group of normal subjects and their fatty acid composition determined by capillary gas-chromatography. The superoxide (O₂) release by the same cell preparations in response to formyl-methionyl-leucyl-phenylalanine was also determined following cytochrome c reduction in a microplate assay. A strong negative correlation was found between C18:2 (linoleic acid) (r = -0.703, P -0.01) and C:16:0 (palmitic acid) ( r = -0.569, P = 0.009) and fMLP-stimulated O₂ release, whereas C20:4 (arachidonic acid) correlated Positively ( r = 0.448, P = 0.048). Other fatty acids, namely C12:0, C14:0, C16:1, C18:1, C18:3, C18:4, C20:0, C20:1, C20:2, C20:5, C22:0, C22:1, C22:6, C24:0 and C26:0, were not correlated with O₂. No correlations were found between fatty acid composition and O₂ release from resting cells and from cells stimulated by phorbol-myristate acetate. These results suggest that the fatty acid composition of blood neutrophils may be a critical factor determining the capability of releasing free radicals in response to formylpeptides. Moreover, since a concomitant increase of arachidonic acid and decrease of its precursor linoleic acid has been found in high-responsive neutrophils, the rate of the enzymes of the arachidonic acid biosynthetic pathway (elongases and desaturases) appear to play an important role.     

Evidence for participation of vicinal dithiols in the activation sequence of the respiratory burst of human neutrophils

Phenylarsine oxide (PAO) specifically forms a stable ring complex with vicinal dithiols that can be reversed with 2,3-dimercaptopropanol (DMP). Pretreatment of human neutrophils with micromolar concentrations of PAO inhibited release of superoxide anion (O2-) stimulated by N- formyl-methionyl-leucyl-phenylalanine (FMLP) or phorbol 12-myristate 13- acetate (PMA); the inhibition was reversed with DMP, but not with 2- mercaptoethanol. PAO did not affect O2- release in previously stimulated cells. PAO did not affect the FMLP-induced Ca2+ response, suggesting that PAO affects a postreceptor event that does not modulate the Ca2+ transient. Treatment of isolated membrane or cytosolic fractions with PAO did not change the rates of arachidonate-stimulated O2- production in a cell-free system. Pretreatment of unstimulated neutrophils with PAO inactivated cytosolic protein kinase C (PKC); the inactivation was reversed with DMP. However, PAO did not affect PMA- induced translocation of beta-PKC protein or reduce the PKC activity translocated to the membrane. PAO had no effect on tyrosine kinase activity but inactivated phosphotyrosine phosphatase; stimulus-induced tyrosine phosphorylation of several proteins was markedly enhanced. These results suggest that vicinal dithiols play an essential role in activation of the respiratory burst oxidase. Possible sites for the activity of these essential vicinal dithiols include PKC and the regulatory balance of tyrosine phosphatase activity and tyrosine phosphorylation.     

Primary structure of human C-reactive protein.

The complete amino acid sequence of human C-reactive protein has been established. Distant homologies to C3 homology region in the CH2 domain of IgG and to C3a anaphylotoxin have been noted. No homology to other immunoglobulin homology regions or to the same homology region in other heavy chains was observed. The previously reported homologies between rabbit and human C-reactive protein and protein C1t have been extended and strengthened.     

Respiratory burst oxidase from human neutrophils: purification and some properties.

The respiratory burst oxidase of human neutrophils was purified by "dye-affinity" chromatography over a red agarose column. Electrophoresis of the purified enzyme on NaDodSO4 gel showed a single major band at 64,000-66,000 daltons, together with some minor contaminants. On a nondenaturing gel, the enzyme ran as two closely spaced bands, the faster of which contained flavin. When these two bands were rerun separately on a NaDodSO4 gel, they gave identical patterns, each showing a major band at ca. 65,000 daltons. The specific activity (mean +/- SEM) of the purified enzyme was 8.8 +/- 3.5 mumol of O-2 per min/mg of protein.     

Effect of Cysticercus cellulosae fractions on the respiratory burst of pig neutrophils

Neutrophils, eosinophils and macrophages are cells that interact with invading parasites and naive hosts have been shown to have anti-parasitic activity. The initial reaction of these leukocytes is the generation of reactive oxygen species (ROS) to play in parasite expulsion. The present work was carried out to study the effect of total extract, scolex and membrane fractions from Cysticercus cellulosae on respiratory burst by pig neutrophils. Hydrogen peroxide (H2O2) production by neutrophils incubated with metacestode fractions from C. cellulosae showed an increase of: 190% (total extract), 120% (scolex) and 44% (membrane). High antioxidant catalatic activity (33%, 28%, 28% by total extract, scolex and membrane, respectively) was observed in neutrophils incubated with metacestode fractions, which could be an attempt at self-protection. Scolex and membrane fractions increased the phagocytic capacity of neutrophils (44% and 28%, respectively). On the other hand, total cysticerci did not alter the phagocytosis, possibly due to modifications in membrane function, caused by high ROS production from neutrophils in the presence of total cysticerci. Total fraction from C. cellulosae is toxic for neutrophils as shown by the decrease in phagocytic capacity, probably caused by high levels of ROS formation. The difference in toxicity of total extract, scolex and membrane fractions on neutrophils can be explained by the presence of an antigenic effect of the vesicular fluid in the total extract of C. cellulosae.     

Ethanol-induced malfunction of neutrophils respiratory burst on patients suffering from alcohol dependence

Background: Polymorphonuclear, neutrophil granulocytes (PMN) play a major role in the control of infections, and people who abuse alcohol are susceptible to infections. Resistance against infections ensues intracellularly following initial phagocytosis of microorganisms with the oxygen‐dependent respiratory burst, the key enzyme of which is the respiratory burst oxidase, whereby oxygen radicals are produced for microbial destruction. To date there is insufficient information available in connection with the process of impaired defence against infection in patients suffering from alcohol dependence. Therefore, our investigation was carried out to determine the influence of alcohol exposition on the formation of oxygen radicals and the respiratory burst. Methods: 4.5 ml of whole blood was taken from 10 healthy adults and 10 patients suffering from alcohol dependence. An additional 3.5 ml of whole blood was taken from the alcoholic patients for determination of the blood alcohol concentration. The respiratory burst of PMN was tested using the Four‐Colour‐Continuous Flow Cytometer. Each experimental procedure consisted of 4 test samples [negative controls, Escherichia coli, FMLP‐supplement (N‐formyl‐l‐methionyl‐l‐leucyl‐l‐phenylalanin), PMA‐supplement (phorbol‐12‐myristate‐13‐acetate)]. Differing concentrations of ethanol were also introduced to each of the tests performed (0.20 to 4.00 g/l). Results: Ethanol revealed a marked decrease of burst activity in those patients suffering from alcoholism with increased alcohol concentration. A dependence between the burst activity and the ethanol concentration was seen to be statistically significant. This effect was only evident after stimulation with E. coli and FMLP in those patients with alcohol dependence. Conclusion: The results presented in this study show an impairment in the function of PMN in those patients addicted to alcohol due to the decrease in burst activity. In view of the results of the different stimuli, the second‐messenger effects were not evident. A clarification of this phenomenon could well be assumed as an allosteric receptor effect on the burst oxidase, namely, a direct effect on the phagocytosis interaction between circulating granulocytes and causative organisms.     

Increased respiratory burst activity of neutrophils in patients with aplastic anemia: effects of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor.

The superoxide (O2-)-releasing capacity in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) and the priming effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) and granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on FMLP-induced O2-release were investigated in neutrophils from 13 patients with aplastic anemia (AA). The O2(-)-releasing capacity of AA neutrophils (0.85 +/- 0.36 nmol/5 min/1 x 10(5) cells, n = 13) was significantly (p < 0.01) increased as compared with that of normal neutrophils (0.24 +/- 0.12 nmol/5 min/1 x 10(5) cells, n = 17). There was no close relationship between the O2(-)-releasing capacity and the peripheral blood neutrophil count or the plasma concentration of C-reactive protein. The plasma concentrations of G-CSF and GM-CSF were not elevated to the detectable levels (< 0.1 ng/ml and < 0.2 ng/ml, respectively) in all patients tested. FMLP-induced O2(-)-release was further enhanced by pretreatment of cells with rhG-CSF or rhGM-CSF for 10 min at 37 degrees C, except that no significant priming by rhG-CSF was observed in five patients. The priming effect of rhGM-CSF was consistently greater than that of rhG-CSF in all patients. The i.v. administration of rhGM-CSF (6 micrograms/kg body weight/day) to one patient resulted in an increase in neutrophil O2(-)-release stimulated by FMLP. These findings indicate that neutrophils from AA patients are already primed in vivo for enhanced release of O2- and that these neutrophil functions are further potentiated by rhG-CSF or rhGM-CSF.     

Decrease of respiratory burst in neutrophils of patients with ankylosing spondylitis by combined radon-hyperthermia treatment.

OBJECTIVE: To define the respiratory burst activity of neutrophils, the total anti-oxidative status of plasma, and the parameters of systemic inflammation in patients with ankylosing spondylitis (AS) before and after a combined radon-hyperthermia treatment in the thermal tunnels of B?ckstein-Bad Gastein in Austria. METHODS: In 20 patients with AS the effects of a total of 15 hours of radon-hyperthermia-treatment spread over a period of three weeks were studied. The respiratory burst activity of neutrophils was measured fluorometrically using dichlorofluorescein diacetate, the total anti-oxidant status was measured using azinodiethyl-benzthiazoline-sulphonate, and inflammation parameters were determined by routine laboratory assays. RESULTS: Before treatment, the basal neutrophil respiratory burst in patients (n = 20) was 409 +/- 62 fluorescence arbitrary units (AU; mean +/- SEM) and 359 +/- 37 AU in controls (n = 9; p > 0.5); the stimulated respiratory burst (fMet-Leu-Phe, 10(-6) M) was 1,027 +/- 133 AU in patients and 1,152 +/- 218 AU in controls (p > 0.5). After treatment, the basal neutrophil respiratory burst in patients (n = 19) was 137 +/- 16 and in controls it was 174 +/- 35 AU (n = 8; p > 0.1); the stimulated respiratory burst was 670 +/- 66 and 1,305 +/- 82 AU, in patients and controls respectively (p < 0.001). No effects of treatment on the total anti-oxidant status of the plasma or on the parameters of inflammation were detected. CONCLUSION: Combined radon-hyperthermia treatment reduces the respiratory burst activity of the blood circulating neutrophils in patients with AS. If respiratory burst activity from the neutrophils plays a role in the pathophysiology of ankylosing spondylitis, the observed reduction may be related to the beneficial effects of radon-hyperthermia treatment.