NAD(P)H-dependent superoxide production by phagocytic vesicles from guinea pig and human granulocytes

HIV type 1 infection of human macrophages induces an upregulation of manganese superoxide dismutase gene that may protect cells from death

It has been previously demonstrated that HIV-1 infection induces a downregulation of MnSOD transcription in CD4+ lymphocytes. Using clinical isolates of macrophage-tropic HIV-1 strains we report here that conversely, purified normal human monocyte-derived macrophages (MDMs) overexpress the manganese superoxide dismutase (MnSOD) gene in response to infection and viral replication. This upregulation of MnSOD gene expression is concomitant with tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) production and treatment of HIV-1-infected MDMs with a specific transcriptional inhibitor of TNF-alpha synthesis counteracts the HIV-1-induced MnSOD gene activation. Moreover, TNF-alpha but not IL-6 addition mimicks the effects of HIV-1 infection on MnSOD gene regulation in normal MDM cultures. These observations strongly suggest that the MnSOD gene induction detected in HIV-1-infected MDMs is triggered by TNF-alpha produced in culture supernatants in parallel to HIV-1 particle release. In contrast to MnSOD, HIV-1 infection or replication in human MDMs has no effect on copper-zinc superoxide dismutase (Cu/ZnSOD) gene expression.

Amplification of superoxide anion generation in phagocytic cells by HIV-1 infection

Amplification of superoxide (O2-) generation by HIV-1 infection was examined in two human myeloid-monocytic cell lines. The level of O2- generation in HL-60 after infection became significantly higher than that of the steady-state. A similar phenomenon was also shown in U937, but only after acquisition of O2- generation ability by differentiation to macrophages. By means of the NADPH oxidase-coupled responses in infected cells, we reconstituted the O2(-)-generating machinery in cell-free system. The results suggested that cytosolic factor(s) exerted by infection might be responsible for the amplification of O2- generation. Thus, HIV-1 infection could elevate the level of oxidative stress in macrophages which might play an important role in disease progression.

The superoxide-forming enzymatic system of phagocytes

The formation of oxygen-derived free radicals by the phagocytes (neutrophils, eosinophils, monocytes and macrophages) is catalysed by a membrane-bound NADPH oxidase which is dormant in resting cells and becomes activated during phagocytosis or following interaction of the cells with suitable soluble stimulants. This enzyme is under investigation in many laboratories but its molecular structure remains to be clarified. Possible components such as flavoproteins, cytochrome b558, and quinones have been proposed on the basis of enzyme purification studies, effects of inhibitors, kinetic properties and analysis of genetic defects of the oxidase. An extensive discussion of the evidence for the participation of these constituents is reported. On the basis of the available information on the structure and the catalytic properties of the NADPH oxidase, a series of possible models of the electron-transport chain from NADPH to O2 is presented. Finally, the triggering mechanism of the respiratory burst is discussed, with particular reference to the stimulus-response coupling and the final modification(s) of the oxidase (phosphorylation, assembly, change of lipid environment, etc.) which are involved in its activation.

Histoplasma capsulatum fails to trigger release of superoxide from macrophages

The yeast form of the dimorphic fungus Histoplasma capsulatum survives within macrophages after phagocytosis. To do so, it must avoid, inhibit, or resist a variety of toxic oxygen metabolites. Using ferricytochrome c reduction to assay superoxide release, we examined the response of mouse macrophages to the yeast form of various H. capsulatum strains. Doses of zymosan as low as 20 particles per macrophage elicited superoxide, whereas H. capsulatum failed to induce superoxide even at 160 yeast cells per macrophage. This phenomenon was observed with two virulent strains of H. capsulatum (G217B and G186A) and with an avirulent variant of G186A. Over a 15- to 150-min observation period, zymosan stimulated increasing reduction of ferricytochrome c, but H. capsulatum did not. When added concurrently with zymosan, H. capsulatum had no effect on superoxide production. Therefore, H. capsulatum was unable either to inactivate the oxygen radical or inhibit host cell superoxide response to other competent stimuli. Enzymatically generated superoxide reduced ferricytochrome c even in the presence of H. capsulatum, again implying that the organism does not readily inactivate superoxide. This experiment also demonstrated that the yeast did not interfere with the assay used. Thus, rather than inhibiting superoxide generation or inactivating the anion, H. capsulatum yeast cells appear to avoid the toxic effects of superoxide by failing to trigger its release.

NADPH and "cocktails" containing polyarginine reactivate superoxide generation in leukocytes lysed by membrane-damaging agents

Human blood leukocytes generated large amounts of superoxide (O2-) following stimulation by certain "cocktails" of soluble agents consisting of poly-L-arginine (PARG), phytohemagglutinin, the chemotactic peptide formyl-methionyl-leucyl-phenylalanine and polyanethole sulfanote (liquoid). A variety of cytochalasins, which markedly boosted O2- generation by the soluble cocktails, markedly depressed luminol-dependent chemiluminescence (LDCL) which had been induced either by opsonized streptococci or by soluble agents. Glutathione, which totally reversed the inhibition of LDCL induced by cytochalasin A, failed to reverse the inhibition of LDCL induced by cytochalasin B. Generation of O2- by all the soluble agents employed, except PMA, was strongly inhibited either by the omission of extracellular calcium and magnesium or by treatment with the calcium blocker TMB-8. Generation of O2- was enhanced following stimulation of leukocytes with soluble agents if the cells had been exposed to slightly hypotonic buffers. Leukocytes, which had been preincubated for short periods (5 min) with PARG, saponin, digitonin, or lysolecithin (LL) and which lost their viability, and their O2- and LDCL-generating capacities following stimulation by soluble agents containing cytochalasin B, nevertheless regained these activities by the addition of NADPH. It is suggested that the lytic agents induced the leakage out of NADPH rather than acting as inactivators of the oxidase in the leukocyte membranes. Prolonged incubation of leukocytes with lytic agents failed to allow restoration, by NADPH, of the generation of SOD-inhibitable O2- generation. Since PARG acted both as a cytolytic agent and as a inducer of O2- generation, we postulate that lytic agents might also act as "primers" of the nascent membrane oxidase which could, however, be further potentiated and activated by soluble agents acting in "multiple hits," PARG could be totally replaced either by LL or by digitonin in the generation of O2- provided that both PHA and cytochalasin B were present in the reaction mixtures. We suggest that the various ingredients of the soluble "cocktails" may help to assemble components of the NADPH oxidase. Such an assembly and regulations are prerequisite for stimulation of the NADPH oxidase and the generation of oxygen radicals in leukocytes.

Activation-associated alterations in neutrophil pyridine nucleotide levels: a potential regulatory role for calcium and calmodulin

The concentration of NADP + NADPH in resting human neutrophils has been measured to be 24.0 +/- 2.7 X 10(-18) mol/cell. Upon activation with opsonized zymosan A, phorbol myristic acetate or N-formylmethionyl-leucylphenylalanine, neutrophil NADP + NADPH pools increase to 80.5, 84.0, and 54.0 X 10(-18) mol/cell, respectively. These increases in pyridine nucleotide concentration are blocked by the addition of the calcium antagonist 8-(N,N-dimethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride, while calcium ionophore A23187, in the presence of calcium, will trigger the increase in the absence of other stimuli. Calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide also inhibit stimulus-induced increases in the NADP + NADPH pool. These studies are interpreted as suggesting a role for calcium and calmodulin, and possibly protein kinase C in the regulation of pyridine nucleotide concentration in the activated neutrophil.

Protein phosphorylation in intact pig leukocytes

The phosphorylation of proteins in intact pig polymorphonuclear leukocytes loaded with H3(32)PO4 was investigated by two-dimensional gel electrophoresis and subsequent autoradiography. The incorporation of 32P into at least 17 proteins began to increase and into one to decrease, relative to resting cells, upon exposure of the cells to phorbol 12-myristate 13-acetate. These changes in the autoradiographic patterns were accompanied by changes in the protein patterns obtained by staining with Coomassie brilliant blue, including the appearance, the acidic shift and the increase or decrease of the intensity of the spots. Among these proteins, Mr = 64 000, 31 000, 22 000, 21 000, 18 000 and 13 000 proteins were correlated well with the superoxide anion production of the cells in respect to the time-courses and the dose-responses. By taking the effects of EGTA into consideration, the phosphorylation of Mr 64 000 and 21 000 proteins, of which the latter was identified as the light chain of myosin, seemed to be involved in the signal-transmission mechanism of the induction of the NADPH oxidase responsible for the 'respiratory burst'. These two proteins were also phosphorylated in the cells stimulated by NaF or oil droplets opsonized with IgG.

Co-localization of superoxide generation and NADP formation in plasma membrane fractions from human neutrophils

In order to resolve discrepancies in the literature concerning the subcellular localization of NADPH oxidase, we disrupted human neutrophils by nitrogen cavitation and fractionated the subcellular organelles on a discontinuous sucrose density gradient. The lightest fraction was 20- to 40-fold enriched for plasma membranes as determined by the marker enzymes alkaline phosphatase and phosphodiesterase I as well as by the ratio of lipid phosphorus to protein. There was a significant decrease in the specific activities of the granule markers myeloperoxidase, lysozyme, and beta-glucuronidase. An intermediate fraction was enriched in membrane markers but not to the extent the lightest fraction was enriched. This fraction contained more granular contamination, as shown by the marker enzymes. In contrast, the densest bands of the gradient were enriched for granule markers with little contamination by plasma membrane. Superoxide generation and NADP formation were primarily associated with the two membrane-enriched fractions from polymorphonuclear leukocytes stimulated with phorbol myristate acetate. The NADP formation associated with a dense granule fraction observed previously in our laboratory was probably due to a cyanide-stimulated oxidation of NADPH by myeloperoxidase.

Superoxide, superoxide dismutase and the respiratory burst

Phagocytes undergo a sharp burst of oxygen consumption when engulfing bacteria. This oxygen is enzymatically reduced to toxic metabolites which are essential to the bactericidal action of the cell. Oxygen metabolites formed in this burst as well as other intermediates formed in biological reduction reactions do not selectively reserve their toxicity for microorganisms. Cells help to guard their organelles against the toxic effects of oxygen by producing intracellular enzymes such as superoxide dismutase. Though superoxide dismutase is found in relatively high concentrations inside cells, there are only small amounts in extracellular fluids. This may account for some of the local tissue damage surrounding aggregates of neutrophils in inflammatory reactions. A pharmacological preparation of superoxide dismutase has shown efficacy in preventing some of the pathological changes seen in degenerative arthritis.

Electrophoretic isolation of a membrane-bound NADPH oxidase from guinea-pig polymorphonuclear leukocytes

Electrophoretic isolation of a membrane-bound NADPH oxidase of guinea-pig polymorphonuclear leukocytes was attempted with the O2- -generating membranes of cells unstimulated or stimulated with C3b-zymosan or sodium dodecyl sulfate, and also with the phagosomes isolated from the phorbol myristate acetate-coated latex particle-phagocytosing cells. When these vesicles were subjected to discontinuous polyacrylamide gel electrophoresis in the presence of Triton X-100 and then assayed for NADPH-Nitroblue tetrazolium reducing activity, the activity was detected by the appearance of a single, blue band of the reduced dye on the gel, independent of the source of vesicles. In addition, the enzyme was able to generate O2- and its activity was significantly augmented with the homologous liver microsomal cytochrome b5. Its activity was heat-labile and inactivated by N-ethylmaleimide and p-chloromercuribenzene sulfonate. The enzyme, with an apparent molecular weight of 150 000, in the phagosomes was easily susceptible to limited proteolysis by trypsin and formed an active fragment with a molecular weight of 70 000, accompanying the loss of O2- -generating activity of the vesicles.

Ca2+ flux as an initial event in phagocytosis by rat Kupffer cells

Ca2+ uptake by monolayer cultures of rat Kupffer cells was strongly stimulated immediately after contact with phagocytosable material, e.g. zymosan particles. The intensity of the luminol-mediated chemiluminescence following zymosan addition was dependent on extracellular Ca2+; addition of the Ca2+-ionophore A 23187 did not further increase the zymosan-elicited response. The superoxide-mediated chemiluminescence was not inhibited by indomethacin but could be suppressed by compounds known to inhibit Ca2+-calmodulin-dependent reactions. Analysis of their efficiency, however, suggests that the O-2 production is mediated by Ca2+ rather than Ca2+-calmodulin and that the inhibitors exert another, e.g. membrane-directed influence.

Lung macrophage defense responses during suramin-induced lysosomal dysfunction

Lysosomes form an integral part of the degradative mechanisms of the phagocytic cells. Mice were injected with suramin, a lysosomotrophic drug, to investigate the effects of lysosomal pathology on the cell biology and in situ bactericidal activity of the pulmonary macrophage. Treatment with suramin resulted in marked alterations in the cell biology of the macrophage: (i) increased vacuolization and protein content, (ii) suppressed intracellular phagosome-lysosome fusion, (iii) decreased activity of the lysosomal enzymes beta-glucuronidase and N-acetyl-glucosaminidase, and (iv) enhanced exocytosis of acid phosphatase during phagocytosis. Addition of suramin, in vitro, to cell lysates resulted in a reduction in the catalytic activities of acid phosphatase, beta-glucuronidase, and N-acetyl-glucosaminidase; thereby suggesting that selective interaction, in vivo, between suramin and lysosomes containing beta-glucuronidase and N-acetyl-glucosaminidase may have occurred. Plasma membrane 5'-nucleotide phosphodiesterase activity was increased in macrophages recovered from suramin-treated animals. Although the "resting-state" reduction of nitroblue tetrazolium (NBT) was lower in these macrophages, cells stimulated by a phagocytic challenge demonstrated normal increases in NBT reduction. Phagocytosis, in vitro, and pulmonary bactericidal activity were not altered. These data demonstrate that suramin altered numerous aspects of the phagocyte's lysosomal system. Despite these changes in the cell biology of the pulmonary macrophage, the cell's defense functions were not reduced.

Genetic disorders of leukocyte function: what they tell us about normal antimicrobial mechanisms of human phagocytic cells

Analysis of three inherited defects of granulocyte function (Chediak-Higashi Syndrome, CHS; Chronic Granulomatous Disease, CGD; Myeloperoxidase Deficiency, MPO) has highlighted critical events for the antimicrobial function of these cells and placed others in perspective. Prompt phagosomal fusion may be more important for digestion of organisms rather than killing as indicated by the mild bactericidal defects in the CHS. The formation of O2- and H2O2 during the phagocytic respiratory burst is central for the broad antimicrobial activity of granulocytes. MPO, on the other hand, while perhaps normally participating in granulocyte antimicrobial action, appears to be essential only for the effective killing of eukaryotic organisms such as certain fungal strains. While the non-oxidative killing mechanism of neutrophils have stimulated much recent interest and were the first to be defined no specific inherited defects have been discovered which are clinically important. Genetic disorders of macrophage effector function remain to be clearly defined as do those of eosinophils. The lessons learned from the study of the granulocyte defects discussed have provided both the technology and approach to the analysis of the antimicrobial and cytocidal mechanisms of these important phagocytic cells.

Selective enrichment of NADPH oxidase activity in phagosomes from guinea pig polymorphonuclear leukocytes

Recent studies have demonstrated that the activated NADPH oxidase, the enzyme responsible for the stimulation of O2 consumption with O2 formation during phagocytosis, is located in the plasma membrane of leukocytes. The present work deals with whether the activation induced by phagocytosis involves the enzyme of the entire membrane or only that of the portion of the membrane that interacts with the phagocytosable particle and forms the phagosome. The results presented show that the activity of the NADPH oxidase of phagosomal membrane, isolated by centrifugation of homogenates on discontinuous sucrose gradients, is increased 12.6-fold with respect that of homogenate. In contrast, the activities of 5'-nucleotidase and of acid p-nitrophenyl phosphatase, enzyme markers of the plasma membrane not activated during phagocytosis and uniformly distributed on the entire membrane, are increased only about three-fold with respect to that of homogenate. These results indicate that during phagocytosis and activation of NADPH oxidase is a segmentary response that involves only the enzyme that forms the phagocytic vacuole. This fact is relevant for the function of toxic intermediates of oxygen reduction that are discharged in direct contact with the engulfed agent.