The H2O2-production by polymorphonuclear leukocytes during phagocytosis

Protein Thiol Redox Signaling in Monocytes and Macrophages

SIGNIFICANCE

Monocyte and macrophage dysfunction plays a critical role in a wide range of inflammatory disease processes, including obesity, impaired wound healing diabetic complications, and atherosclerosis. Emerging evidence suggests that the earliest events in monocyte or macrophage dysregulation include elevated reactive oxygen species production, thiol modifications, and disruption of redox-sensitive signaling pathways. This review focuses on the current state of research in thiol redox signaling in monocytes and macrophages, including (i) the molecular mechanisms by which reversible protein-S-glutathionylation occurs, (ii) the identification of bona fide S-glutathionylated proteins that occur under physiological conditions, and (iii) how disruptions of thiol redox signaling affect monocyte and macrophage functions and contribute to atherosclerosis. Recent Advances: Recent advances in redox biochemistry and biology as well as redox proteomic techniques have led to the identification of many new thiol redox-regulated proteins and pathways. In addition, major advances have been made in expanding the list of S-glutathionylated proteins and assessing the role that protein-S-glutathionylation and S-glutathionylation-regulating enzymes play in monocyte and macrophage functions, including monocyte transmigration, macrophage polarization, foam cell formation, and macrophage cell death.

CRITICAL ISSUES

Protein-S-glutathionylation/deglutathionylation in monocytes and macrophages has emerged as a new and important signaling paradigm, which provides a molecular basis for the well-established relationship between metabolic disorders, oxidative stress, and cardiovascular diseases.

FUTURE DIRECTIONS

The identification of specific S-glutathionylated proteins as well as the mechanisms that control this post-translational protein modification in monocytes and macrophages will facilitate the development of new preventive and therapeutic strategies to combat atherosclerosis and other metabolic diseases. Antioxid. Redox Signal. 25, 816-835.

Interaction of Aspergillus fumigatus Spores with Human Leukocytes and Serum

Serum was necessary for optimal phagocytosis of Aspergillus fumigatus spores by human leukocytes, and its opsonic capacity was greatly diminished by heat inactivation (56 C, 30 min). A germination assay, described in this report, was developed to study the fate of phagocytized spores. After incubation for 3 hr with normal leukocytes and serum, spores ingested by peripheral blood neutrophils and monocytes remained viable. Since we had previously found that myeloperoxidase (MPO), a lysosomal enzyme of human neutrophils and monocytes, exerted fungicidal activity against Candida albicans when combined with H(2)O(2) and chloride or iodide, the effects of these substances on A. fumigatus spores were examined. Spore viability was not impaired by MPO alone, H(2)O(2) alone, or KI alone, but high concentrations of KI and H(2)O(2) in combination caused marked inhibition of subsequent germination. MPO imparted fungicidal activity to concentrations of KI and H(2)O(2) that lacked any effect in its absence. NaCl, in combination with MPO and H(2)O(2), was far less effective than the iodide salt against A. fumigatus. The relative ineffectiveness of chloride in this system could underly the apparent inability of human neutrophils to kill ingested A. fumigatus spores, despite their competence to kill C. albicans.

Drug potentiation of macrophage function

The mechanism by which macrophages kill facultative intracellular parasites is not known. A test system is described utilizing human macrophages derived from blood monocytes and the opportunistic pathogen Listeria monocytogenes. In this system, bacterial killing was impaired under hypoxic conditions. Under aerobic conditions, addition of Clofazimine (B663), a phenazine derivative effective in the treatment of human leprosy, potentiated the killing of Listeria by macrophages. Potentiation occurred at drug concentrations usually attainable in man and which are not directly injurious to the bacteria. The enhanced bactericidal activity occurred only in the presence of oxygen; the drug induced increased leukocyte oxygen consumption which was insensitive to cyanide.

Effect of sodium azide on hydrogen peroxide production by zymosan-activated human neutrophils

Stimulated neutrophils (PMNs) produce large quantities of superoxide anion, which is the precursor for hydrogen peroxide (H2O2). We developed a new fluorimetric assay to measure the H2O2 released by zymosan A-activated PMNs utilizing the oxidation of p-hydroxyphenylacetic acid by H2O2 to its fluorescent dimer in the presence of horseradish peroxidase. Zymosan-activated PMNs isolated from nine healthy volunteers and 20 patients with acute hypoxemic respiratory failure (AHRF) released after 90 min 2.3 +/- 0.3 and 2.4 +/- 1.3 nmol H2O2/10(6) PMNs, respectively. Inhibition of the heme enzymes by 1.0 mM sodium azide (NaN3) increased the H2O2 production to 21.6 +/- 4.4 nmol H2O2/10(6) PMNs in the control group (P less than 0.001), and to 22.5 +/- 14.7 nmol H2O2/10(6) PMNs in patients with AHRF (P less than 0.001). Incubation temperature, room temperature or 37 degrees C, did not change the total amount of H2O2 produced after 90 min by zymosan-activated PMN. Addition of NaN3 improved both the sensitivity and reproducibility of the measurement of H2O2 and allowed detection of H2O2 released by PMNs with coefficients of variation of less than 5% at PMN concentrations as low as 0.1 x 10(6) cells/ml. The amount of H2O2 released by activated PMNs did not distinguish healthy controls from patients with AHRF.

A semi-automated micro-assay for H2O2 release by human blood monocytes and mouse peritoneal macrophages

H2O2 secreted by mononuclear phagocytes can be detected by monitoring the horseradish peroxidase-catalyzed oxidation of fluorescent scopoletin. This technique has been adapted to a semi-automated micro-scale with the aid of automatic fluorescence and absorbance micro-culture plate readers to measure H2O2 and protein, respectively, in the same culture wells. With these adaptations the assay can accurately and precisely detect as little as 0.1 nmol H2O2 or 1 microgram cell protein, permitting the calculation of specific secretion (nmol H2O2/mg cell protein) from as few as 2 X 10(4) human blood monocytes or mouse peritoneal macrophages. Cumulative H2O2 secretion in individual wells may be recorded non-destructively at frequent intervals for time course measurements. Less than 1 min is required to record the fluorescence in all 96 wells of a micro-culture plate. The assay is highly reproducible, with standard deviations for triplicates typically less than 5-10% of the mean, and gives values in close agreement with those obtained in 10-fold larger samples by previous methods. Using this assay it is feasible to process 1000 samples per day, with order of magnitude savings in labor, cells, sera, media, cytokines, and reagents compared to earlier forms of the assay. The assay is useful in evaluating the cellular effects of cytokines and for assaying their activity in chromatographic fractions and hybridoma cultures. We are currently using the assay to monitor the administration of interferon-gamma to patients with neoplasia.

Measurement of oxidizing radicals by polymorphonuclear leukocytes

O2 radicals are important in health and disease. The most commonly used ways of identifying O2 radicals in PMN are described above. Several shortcomings exist in these methods reflecting the unusual, complex nature of O2 radical biochemistry. Some general principles include (1) O2 radicals are very short-lived, reacting with many other compounds and each other quickly. (2) There are no highly specific assays for O2 radicals. (3) Highly specific scavengers of O2 radicals also do not exist. (4) No methods have been found to detect and quantitate O2 radicals in vivo. (5) Solubility and membrane permeability of various scavengers and/or test reagents may affect the measurement of O2 radicals in PMN and other biological systems. In general, the best approach to measurement of O2 radicals involves using the best assay available and showing that the reaction is inhibited by scavengers in proportion to their reactivity with the specific O2 radical being assayed.

Oxidative metabolism of chicken polymorphonuclear leucocytes during phagocytosis

The oxidative response to phagocytosis by chicken polymorphonuclear leucocytes was investigated as compared to guinea pig polymorphonuclear leucocytes. The polymorphs from both species respond to phagocytosis with an increased oxygen consumption, an increased generation of O2 and H2O2, and an increased oxidation of glucose through the hexose monophosphate shunt. The rate of oxygen consumption, and generation of O2- and H2O2 by phagocytosing chicken polymorphonuclear leucocytes is considerably lower than with phagocytosing guinea pig polymorphonuclear leucocytes. By contrast, the extent of hexose monophosphate shunt stimulation in chicken polymorphs is comparable to that of guinea pig polymorphs. Evidence is presented suggesting that H2O2 is preferentially degraded in chicken cells through the glutathione cycle, whereas catalase and myeloperoxidase are the two main H2O2 degrading enzymes in guinea pig cells. The 20,000 g fraction of the postnuclear supernatant of chicken polymorphs contains a cyanide-insensitive NADPH oxidizing activity which is stimulated during phagocytosis. Similar properties for the NADPH oxidizing activity of guinea pig polymorphs have been previously reported. It is concluded that the metabolic burst of phagocytosing chicken polymorphonuclear leucocytes is qualitatively similar to that of guinea pig polymorphonuclear leucocytes, but the latter cells are more active in all the biochemical parameters that have been measured. The difference in the H2O2 degradation pathways between the two species is accounted for by the lack of myeloperoxidase and catalase in chicken polymorphs.

Phagocytosis: a review

Primitive unicellular organisms depend greatly on internalization of particulate matter for nourishment. In metazoa, this process is further developed to play a major role in mechanisms of defense. This review analyzes, mainly in mammalian systems, the various phenomena surrounding the phagocytic act. Much of the emphasis is placed on experimental work which has recently elucidated some of its features. Both the structural and functional aspects of phagocytosis are considered throughout the review, which is subdivided into an examination of chemotaxis and the various agents inducing it, the mode of recognition of particles to be phagocytized, and the mechanisms of ingestion. The last includes a discussion of the possible means whereby recognition is translated into ingestion, the modes of adhesion of particles onto the surface of phagocytes, the formation and fusion of pseudopodia during engulfment and ingestion, and process and significance of degranulation. In addition, the metabolic changes in phagocytes during the processes of chemotaxis, ingestion, and digestion are described. A discussion of the various ways phagocytes may destroy microorganisms incorporates an appreciation of the importance of the microbicidal action of the acidic environment of the phagosome, the various lysosomal contents, hydrogen peroxide, superoxide, singlet oxygen, and chemiluminescence. The interdependence and interrelationship of the induction and cooperation of these mechanisms are examined.

Purification of human granulocyte catalase in chronic myeloid leukemia

Human granulocyte catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase, EC 1.11.1.6) was purified from chronic myeloid leukemia cells. The purification procedure included heat precipitation, ammonium sulphate fractionation, DEAE-Sephadex chromatography, gel chromatography on Sephadex G-200 and isoelectric focusing with an approximate yield of 30% and a 1000-fold purification. The molecular weight of the subunit obtained by sodium dodecyl sulphate electrophoresis was 65 800. So20,w was 11.6 +/- 0.24. The pH-optimum was 6.6-6.7 and the spectrum showed a major peak at 405 nm and shoulders at 500, 540 and 625 nm typical for catalase. The electrophoretic mobility was towards the anode at pH 8.6 and identical to normal granulocyte and erythrocyte catalase. These three species of catalase gave the reaction of identity on immunodiffusion and crossed immunoelectrophoresis. The content of catalase and its activity of isolated granulocytes were approximately identical in normal and chronic myeloid leukemia granulocytes while the specific activity of leukemic catalase was higher than normal. No difference in catalase content was found between mature and immature leukemic granulocytes.

Characteristics of the phagocytic process assessed by Coulter Counter

The phagocytosis in suspensions of heat-killed yeast cells, Saccharomyces cerevisiae, by human polymorphonuclear leucocytes was studied in vitro by means of an electronic particle counter, the Coulter Counter, and a 100-channel pulse-height analyzer, the Channelyzer. The two cell populations were separated from each other electronically by the Channelyzer. Phagocytosis was recorded as disappearence of yeast cells. Concomitantly, aggregation and swelling of the PMN-cells were observed, which increased with the concentration of the prey. The process could be inhibited by cytochalasin B and iodoacetamide. With the latter inhibitor, the analysis of the kinetics showed that ingestion, but not adhesion, was affected. The ingestion of yeast cells was augmented on increase of the initial ratio between the number of yeast and PMN cells to around 5:1, but was then reduced on further increase. A ratio of 2:1 and a reaction time of 30 min seemed suitable for studying the phagocytic process. First-order kinetics were obeyed under these circumstances.

Function of granulocytes with deficient myeloperoxidase-mediated iodination in a patient with generalized pustular psoriasis

The granulocytes of a patient with generalized pustular psoriasis (GPP) were found to have impaired ability to fix iodine after ingestion of yeast particles. Since hexose monophosphate shunt (HMS) activity was increased and the contents of 3 other lysosomal enzymes, beta-glucuronidase, N-acetyl-beta-glucosaminidase and lysozyme, were within normal range, the impaired iodination appeared to be due to a selective defect of myeloperoxidase (MPO) activity within the phagocytic cells. The deficient iodination was accompanied by a decreased intracellular killing of E. coli and C. albicans. Since hexose monophosphate shunt activity was enhanced and azide and cyanide inhibited the intracellular killing of E. coli only moderately, the patient's granulocytes may possess azide- and cyanide-resistant, MPO-independant microbicidal systems coupled to the oxidative metabolism. Assessment of granulocyte iodination and enzyme contents of the relatives of the patient revealed no hereditary transmission. Since GPP is characterized by the development of subcorneal pustules containing granulocytes, the MPO-deficiency may be the cause of or enhance the development of the disease.

Ascorbate and phagocyte function

Scorbutic guinea pig neutrophils (PMN) were found to produce H2O2 and kill Staphylococcus aureus as well as control PMN, suggesting that ascorbate does not contribute significantly to phagocyte H2O2 production or bacterial killing. Total and reduced ascorbate contents of human PMN was observed to fall upon phagocytosis, whereas dehydroascorbate increased to a lesser extent. These observations are consistent with the view that ascorbate constitutes a functional part of the PMN's redox-active components and may thus function to protect cell constituents from denaturation by the oxidants produced during phagocytosis.

Chlorinating ability of human phagocytosing leucocytes

The course of chlorination in neutrophilic granulocytes has been shown. The process of 36Cl incorporation occurs during and after the engulfment of bacteria by granulocytes. Incorported radioactivity was found in insoluble fractions. The myeloperoxidase obtained from neutrophils catalyzes chlorination of protein (bovine serum albumin) and bacteria (Staphylococcus epidermidis) in the presence of hydrogen peroxide and chloride. The products of chlorination are insoluble. Chlorination in neutrophils is inhibited by the iodide and myeloperoxidase inhibitors azide and cyanide. A quantitative method of determination of biological chlorination in cells has been devised.

Peroxidase-mediated mammalian cell cytotoxicity

Lactoperoxidase, in the presence of hydrogen peroxide and iodide is cytotoxic for human and mouse lymphoid cells, and human erythrocytes. Myeloperoxidase, in amounts equivalent to 1.5 x 10(6) neutrophils, readily replaces lactoperoxidase, and allows the substitution of the iodide ion by chloride. The myeloperoxidase-mediated reaction is rapid, and highly efficient, leading to 85-90% cell death in 90 min, as measured by (51)chromium release and dye exclusion. The mixture of granulocytes. monocytes, and lymphocytes present in an inflammatory exudate, and the intimate cell-to-cell association characteristic of cytotoxic phenomena may provide the in vivo requirements for such a system.

In vitro antibody-enzyme conjugates with specific bactericidal activity

IgG with antibacterial antibody opsonic activity was isolated from rabbit antisera produced by intravenous hyperimmunization with several test strains of pneumococci, Group A beta-hemolytic streptococci, Staphylococcus aureus, Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli. Antibody-enzyme conjugates were prepared, using diethylmalonimidate to couple glucose oxidase to IgG antibacterial antibody preparations. Opsonic human IgG obtained from serum of patients with subacute bacterial endocarditis was also conjugated to glucose oxidase. Antibody-enzyme conjugates retained combining specificity for test bacteria as demonstrated by indirect immunofluorescence. In vitro test for bactericidal activity of antibody-enzyme conjugates utilized potassium iodide, lactoperoxidase, and glucose as cofactors. Under these conditions glucose oxidase conjugated to antibody generates hydrogen peroxide, and lactoperoxidase enzyme catalyzes the reduction of hydrogen peroxide with simultaneous oxidation of I(-) and halogenation and killing of test bacteria. Potent in vitro bactericidal activity of this system was repeatedly demonstrated for antibody-enzyme conjugates against pneumococci, streptococci, S. aureus, P. mirabilis, and E. coli. However, no bactericidal effect was demonstrable with antibody-enzyme conjugates and two test strains of P. aeruginosa. Bactericidal activity of antibody-enzyme conjugates appeared to parallel original opsonic potency of unconjugated IgG preparations. Antibody-enzyme conjugates at concentrations as low as 0.01 mg/ml were capable of intense bactericidal activity producing substantial drops in surviving bacterial counts within 30-60 min after initiation of assay. These in vitro bactericidal systems indicate that the concept of antibacterial antibody-enzyme conjugates may possibly be adaptable as a mechanism for treatment of patients with leukocyte dysfunction or fulminant bacteremia.

Hydrogen peroxide utilization in myeloperoxidase-deficient leukocytes: a possible microbicidal control mechanism

Phagocytosis-induced formate and glucose C-1 oxidation by the polymorphonuclear leukocytes of a patient with hereditary myeloperoxidase deficiency was considerably greater than normal. The addition of catalase to the leukocyte suspension was required for optimum formate oxidation. Azide and cyanide increased glucose C-1 oxidation by normal leukocytes but had little or no effect on myeloperoxidase-deficient leukocytes suggesting that these agents normally stimulate glucose C-1 oxidation, in part, by inhibition of myeloperoxidase. It is suggested that the inhibition or absence of myeloperoxidase results in an increased utilization of H(2)O(2) in nonmyeloperoxidase-mediated H(2)O(2)-dependent reactions such as formate oxidation and hexose monophosphate pathway activation. The possibility of a microbicidal control mechanism in which a decrease in the microbicidal activity of myeloperoxidase is offset, in part, by an increase in the nonenzymatic microbicidal activity of H(2)O(2) is considered.

Myeloperoxidase: contribution to the microbicidal activity of intact leukocytes

Azide and, to a lesser extent, cyanide inhibit the microbicidal activity of myeloperoxidase and of intact normal leukocytes, but they have little or no effect on peroxidase-negative leukocytes. The contribution of the azide-sensitive (peroxidase-dependent?) systems to the total microbicidal activity of normal leukocytes is considerable. The azide-insensitive antimicrobial systems are more highly developed in peroxidase-negative leukocytes than in normal leukocytes, thus suggesting an adaptation.

Peroxidase-mediated virucidal systems

Peroxidase (myeloperoxidase or lactoperoxidase), hydrogen peroxide, and a halide such as iodide, bromide, or chloride form a potent virucidal system that is effective against polio and vaccinia viruis, particularly at a low pH. The peroxidase-halide-hydrogen peroxide system may contribute to the host defense against certain viral infections.