The respiratory burst of phagocytosis: biochemistry and subcellular localization

NADPH oxidase in brain injury and neurodegenerative disorders

Oxidative stress is a common denominator in the pathology of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, as well as in ischemic and traumatic brain injury. The brain is highly vulnerable to oxidative damage due to its high metabolic demand. However, therapies attempting to scavenge free radicals have shown little success. By shifting the focus to inhibit the generation of damaging free radicals, recent studies have identified NADPH oxidase as a major contributor to disease pathology. NADPH oxidase has the primary function to generate free radicals. In particular, there is growing evidence that the isoforms NOX1, NOX2, and NOX4 can be upregulated by a variety of neurodegenerative factors. The majority of recent studies have shown that genetic and pharmacological inhibition of NADPH oxidase enzymes are neuroprotective and able to reduce detrimental aspects of pathology following ischemic and traumatic brain injury, as well as in chronic neurodegenerative disorders. This review aims to summarize evidence supporting the role of NADPH oxidase in the pathology of these neurological disorders, explores pharmacological strategies of targeting this major oxidative stress pathway, and outlines obstacles that need to be overcome for successful translation of these therapies to the clinic.

Wound Fluids: A Window Into the Wound Environment?

Wound healing of the skin is a complex biologic process involving temporal interactions between numerous types of cells, extracellular matrix molecules, and soluble factors. The process of repair can be viewed as involving 3 or 4 phases: homeostasis, inflammation, synthesis, and remodeling. These phases occur at different times and differ in their cellular, biochemical, and physiologic requirements. Disruption of one or more of these interactions can significantly interfere with the repair process. Such comorbidities as age, nutrition, immune status, and underlying disease status (eg, diabetes or venous stasis) contribute additional intricacy to the repair process. Because of this complexity, care of chronic wounds remains highly individualized, and it should not come as a surprise that treatment of these wounds as a group with single target therapies have met with only modest success. A major hurdle in the progression toward improved treatment regimens has been the lack of objective biochemical and physiological landmarks that can be used to assess wound status. Collection and biochemical characterization of wound fluids presents the opportunity to noninvasively obtain information reflecting the status of the wound and of specific biomarkers. This review discusses the collection of wound fluid and highlights biomarkers that may be useful to this end.

gp96 expression in neutrophils is critical for the onset of Escherichia coli K1 (RS218) meningitis

Despite the fundamental function of neutrophils (PMNs) in innate immunity, their role in Escherichia coli K1 (EC-K1) induced meningitis is unexplored. Here we show that PMN-depleted mice are resistant to EC-K1 (RS218) meningitis. EC-K1 survives and multiplies in PMNs for which outer membrane protein A (OmpA) expression is essential. EC-K1infection of PMNs increases the cell surface expression of gp96, which acts as a receptor for bacterial entry. Suppression of gp96 expression in newborn mice prevents the onset of EC-K1 meningitis. Infection of PMNs with EC-K1 suppresses oxidative burst by down regulating rac1, rac2 and gp91^phox transcription both in vitro and in vivo. The interaction of loop 2 of OmpA with gp96 is essential for EC-K1-mediated inhibition of oxidative burst. These results reveal that EC-K1 exploits surface expressed gp96 in PMNs to prevent oxidative burst for the onset of neonatal meningitis.

Involvement of red blood cells in the regulation of leukotriene synthesis in polymorphonuclear leucocytes upon interaction with Salmonella Typhimurium

Leukotriene (LT) B4 is the primary eicosanoid product of polymorphonuclear leucocytes (PMNLs). We studied LT synthesis in PMNLs upon interaction with Salmonella enterica serovar Typhimurium. Human PMNLs exposed to Salmonella produced LTs; mostly LTB4 and ω-hydroxy-LTB4. Opsonization with normal serum increased the capacity of S. Typhimurium to induce LT synthesis in PMNLs. Addition of red blood cells (RBCs) alone did not activate LT synthesis in PMNLs but did further increase the Salmonella-induced release of LTs. Priming of PMNLs with lipopolysaccharide before the addition of bacteria potentiated LT synthesis in these cells. The effect was more pronounced in the presence of RBCs. We found that RBCs diminished the effect of exogenously added NO donors on LT synthesis in PMNLs. We conclude that RBCs mediate the activation of LT synthesis in PMNLs exposed to Salmonella bacteria at least in part by regulating the intercellular exchange and metabolism of NO.

Immunostimulatory effects of Uncaria perrottetii (A. Rich.) Merr. (Rubiaceae) vinebark aqueous extract in Balb/C mice

AIMS OF THE STUDY

Crude extract of Uncaria perrottetii (A. Rich.) Merr. vinebark was evaluated for its immunomodulating activity in Balb/C mice. Initially, the immunomodulatory potential of the plant extract was evaluated using in vitro immune response assays at different concentrations of the plant extract (10 μg/mL, 20 μg/mL, 50 μg/mL and 100 μg/mL). Using the optimum concentration determined in the in vitro assays, the protective effect of the plant extract was assessed against drug-induced immunosuppression in vivo.

MATERIALS AND METHODS

For the in vivo experiment, thirty-six (36) mice were divided into 3 groups of 12 mice each: (1) cyclophosphamide drug-induced (30 mg/kg BW) immunosuppressed mice (Cy group) served as the positive control; (2) Uncaria perrottetii extract and Cy-treated mice (U+Cy); and (3) PBS-injected mice as the negative control group [(-) CTRL].

RESULTS

The optimum concentration was determined to be 50 μg/mL in the in vitro assays. At this concentration, Uncaria perrottetii extract stimulated peritoneal phagocyte activation, produced a significant increase in the activity of phagocytic cells from the spleen and promoted splenic cellular proliferation with or without lipopolysaccharide (LPS) when compared with the PBS-treated cells (negative control). Moreover, cells treated with 50 μg/mL of Uncaria perrottetii increased macrophage respiratory burst activity that was comparable to that of the phorbol myristate acetate-stimulated splenic macrophages. In all immune assays undertaken in the in vivo experiment, the Cy-treated mice showed significantly lower response when compared with the PBS-treated mice. Significant improvement in peritoneal cell activation, phagocytic activity and cellular proliferation was exhibited by the U+Cy-treated mice when compared with Cy-injected mice. The extract from Uncaria perrottetii also significantly enhanced respiratory burst and plasma lysozyme activity compared with the Cy-injected mice.

CONCLUSIONS

Based on the results of both in vitro and in vivo trials, Uncaria perrottetii extract has immunopotentiating activities on the innate immunity of Balb/C mice and the extract could potentially reverse the immunosuppressive effects of Cy. However, the potential of the plant as source of bioactive products and metabolites for drug development still has to be fully investigated.

Lack of glucose recycling between endoplasmic reticulum and cytoplasm underlies cellular dysfunction in glucose-6-phosphatase-beta-deficient neutrophils in a congenital neutropenia syndrome

G6PC3 deficiency, characterized by neutropenia and neutrophil dysfunction, is caused by deficiencies in the endoplasmic reticulum (ER) enzyme glucose-6-phosphatase-β (G6Pase-β or G6PC3) that converts glucose-6-phosphate (G6P) into glucose, the primary energy source of neutrophils. Enhanced neutrophil ER stress and apoptosis underlie neutropenia in G6PC3 deficiency, but the exact functional role of G6Pase-β in neutrophils remains unknown. We hypothesized that the ER recycles G6Pase-β-generated glucose to the cytoplasm, thus regulating the amount of available cytoplasmic glucose/G6P in neutrophils. Accordingly, a G6Pase-β deficiency would impair glycolysis and hexose monophosphate shunt activities leading to reductions in lactate production, adenosine-5'-triphosphate (ATP) production, and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Using annexin V-depleted neutrophils, we show that glucose transporter-1 translocation is impaired in neutrophils from G6pc3(-/-) mice and G6PC3-deficient patients along with impaired glucose uptake in G6pc3(-/-) neutrophils. Moreover, levels of G6P, lactate, and ATP are markedly lower in murine and human G6PC3-deficient neutrophils, compared with their respective controls. In parallel, the expression of NADPH oxidase subunits and membrane translocation of p47(phox) are down-regulated in murine and human G6PC3-deficient neutrophils. The results establish that in nonapoptotic neutrophils, G6Pase-β is essential for normal energy homeostasis. A G6Pase-β deficiency prevents recycling of ER glucose to the cytoplasm, leading to neutrophil dysfunction.

Structural organization of the neutrophil NADPH oxidase: phosphorylation and translocation during priming and activation

The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is part of the microbicidal arsenal used by human polymorphonuclear neutrophils (PMNs) to eradicate invading pathogens. The production of a superoxide anion (O2-) into the phagolysosome is the precursor for the generation of more potent products, such as hydrogen peroxide and hypochlorite. However, this production of O2- is dependent on translocation of the oxidase subunits, including gp91phox, p22phox, p47phox, p67phox, p40phox, and Rac2 from the cytosol or specific granules to the plasma membrane. In response to an external stimuli, PMNs change from a resting, nonadhesive state to a primed, adherent phenotype, which allows for margination from the vasculature into the tissue and chemotaxis to the site of infection upon activation. Depending on the stimuli, primed PMNs display altered structural organization of the NADPH oxidase, in that there is phosphorylation of the oxidase subunits and/or translocation from the cytosol to the plasma or granular membrane, but there is not the complete assembly required for O2- generation. Activation of PMNs is the complete assembly of the membrane-linked and cytosolic NADPH oxidase components on a PMN membrane, the plasma or granular membrane. This review will discuss the individual components associated with the NADPH oxidase complex and the function of each of these units in each physiologic stage of the PMN: rested, primed, and activated.

Oxidase activity in cord blood neutrophils: a balance between increased membrane associated cytochrome b558 and deficient cytosolic components

INTRODUCTION

Newborn infants are prone to develop life-threatening pyogenic infections. Alterations in the function of neonatal phagocytes, including the activity of the neutrophil NADPH oxidase, have been suggested as one cause of increased susceptibility to such infections.

METHODS

In the present study, comprehensive analysis of NADPH oxidase enzyme system was performed in cord blood neutrophils from vaginally and cesarean section (CS) delivered, healthy, full-term infants.

RESULTS

Superoxide anion (O(2) (-)) production by intact neutrophils from cord blood in response to soluble stimuli was equal to or increased compared to levels generated by cells from adult controls. In the sodium dodecyl sulfate (SDS) cell-free system, cytosol and plasma membrane from cord blood neutrophils generated O(2) (-) at comparable rates to subcellular fractions from healthy adults. However, mixing experiments demonstrated higher O(2) (-) generation with combination of cytosol from adult controls and membrane from cord blood neutrophils and lower O(2) (-) production with combination of cytosol from cord blood neutrophils and membrane from adult controls. Kinetic parameters for cord blood specimens were no different from those obtained for fractions from adult controls. Quantitative analysis of cytosolic components showed moderately reduced amount of p40-phox, p47-phox, and p67-phox in neutrophils from cord blood. In contrast, cytochrome b(558) content of plasma membrane of cord blood neutrophils was approximately 2-fold higher compared to adult controls.

CONCLUSION

The normal to increased respiratory burst of intact cord blood neutrophils is the result of alterations to oxidase components: increased content of cytochrome b(558) in the plasma membrane and decreased levels of cytosolic components p47-phox, p67-phox, and p40-phox.

A potential role for periplasmic superoxide dismutase in blocking the penetration of external superoxide into the cytosol of Gram-negative bacteria

Superoxide is a key component of the antibacterial weaponry of phagocytes. Presumably, for this reason, strains of Salmonella typhimurium express a periplasmic superoxide dismutase (SOD) that is essential for full virulence. Because most anions cannot easily penetrate lipid membranes, it is thought that the phagosomal superoxide either damages an unknown target on the bacterial surface or reacts with nitric oxide to form peroxynitrite (HOONO), a toxic oxidant that can freely enter bacteria. However, in this study, we tested whether superoxide itself could penetrate membranes. Superoxide that was generated at high pH (>7.5) very slowly reduced cytochrome c that was encapsulated inside lipid vesicles. It did so much more quickly at lower pH (<7). Under the latter conditions, more superoxide was protonated and uncharged (HO2*), and the penetrance of superoxide was proportional to the concentration of this species. The permeability coefficient of HO2* was determined to be 9 x 10(-4) cm sec(-1), just slightly lower than that of water and far higher than the value of the anionic form (O2-, <10(-7) cm sec(-1). When Escherichia coli mutants that lack periplasmic SOD were exposed to super-oxide at pH 6.5, cytosolic fumarase B was damaged. Damage was minimal at higher pH or in strains that contained periplasmic SOD. Thus, in the acidic phagolysosome, superoxide may be able to penetrate and attack cytosolic targets of captive bacteria. This process may contribute to the potency of the oxidative burst. One role of periplasmic SOD may be to avert this damage. In contrast, periplasmic SOD was ineffective at lowering the extracellular super-oxide concentration and, therefore, may have little impact upon HOONO formation.

Transient Association of the Nicotinamide Adenine Dinucleotide Phosphate Oxidase Subunits p47phox and p67phox With Phagosomes in Neutrophils From Patients With X-Linked Chronic Granulomatous Disease

Optimal microbicidal activity of polymorphonuclear leukocytes (PMNs) requires recruitment of a functional nicotinamide adenine dinucleotide phosphate (NADPH) oxidase to the phagosome. In this study, we used a synchronized phagocytosis assay and immunofluorescence microscopy (IFM) to examine the association of cytosolic NADPH oxidase subunits with phagosomes containing opsonized zymosan (OpZ). Ingestion of OpZ began within 30 seconds of particle binding and forming phagosomes were enriched for both F-actin and the actin-binding protein p57. NADPH oxidase subunits p47phox and p67phox were also recruited to forming phagosomes and were retained on mature phagosomes for at least 15 minutes. Colocalization of F-actin, p57, and p47phox on phagosomes was confirmed by immunoblotting. Translocation of p67phox, but not p57, to forming phagosomes was deficient in PMNs lacking p47phox. Surprisingly, we found that in PMNs from six individuals with X-linked chronic granulomatous disease (CGD), p47phox and p67phox accumulated in the periphagosomal area during ingestion of OpZ. However, in marked contrast to normal PMNs, p47phox and p67phox were shed from nascent phagosomes along with F-actin and p57 once OpZ was internalized (≈5 minutes). These data support a model in which flavocytochrome b is required for stable membrane binding of p47phox and p67phox, but not their association with the cytoskeleton or transport to the cell periphery.

Influence of carbon particles on superoxide and hydrogen peroxide radical release during the killing of Mycobacterium bovis by alveolar macrophages

SETTING

Diagnostic bronchoscopy performed on untreated African patients with tuberculosis revealed alveolar macrophages filled with carbon particles. It was postulated that this was the result of excessive inhalation of smoke from domestic fires and the consequent phagocytosis by alveolar macrophages.

OBJECTIVE

To determine whether carbon particles influence the release of superoxide and hydrogen peroxide radicals by the alveolar macrophage during killing of Mycobacterium bovis.

DESIGN

Alveolar macrophages were recovered by bronchoalveolar lavage from adult rabbits and cultured. Experimental macrophages were exposed to M. bovis and carbon particles, controls only to M. bovis. Superoxide release was measured by the superoxide dependent cytochrome C reduction method and hydrogen peroxide release by luminol dependent chemiluminescence. Significance of differences was calculated by Student's t-test for unpaired data.

RESULTS

For superoxide and hydrogen peroxide release, results show a significant difference between the experiments and the controls. Hydrogen peroxide radicals are, however, released at a low constant average median value in the controls.

CONCLUSION

Hydrogen peroxide is not greatly involved in the killing of M. bovis by alveolar macrophages since low concentrations are released in the controls. Ingestion of large amounts of carbon particles decreases the release of superoxide and hydrogen peroxide radicals.

Characterization of 2,3-dihydroxybenzoic acid from Nocardia asteroides GUH-2

Culture filtrates of virulent Nocardia asteroides GUH-2 after growth in acetate minimal medium displayed an absorbance maximum at 320 nm. After isolation by polyamide extraction and anion chromatography, a UV-active compound with this absorbance was shown to be 2,3-dihydroxybenzoic acid (DHB) by nuclear magnetic resonance, gas chromatographic, and mass spectrometric techniques. DHB production under several culture conditions was quantified by a standard high-pressure liquid chromatography assay. Under iron deficiency conditions, N. asteroides GUH-2 excreted up to 11 mg of DHB per liter into the culture medium. No DHB was detected when N. asteroides GUH-2 was grown in an iron-rich medium. With the less virulent strain N. asteroides 10905, DHB was not found under any condition tested.

Differential inhibition of prostaglandin and superoxide production by dexamethasone in primary cultures of rat Kupffer cells

Dexamethasone inhibited the stimulus-induced prostaglandin E2 formation by rat Kupffer cells in primary culture, e.g. after treatment with zymosan, phorbol ester, calcium ionophore A23187, platelet-activating factor or lipopolysaccharide. Prostaglandin E2 production from added free arachidonic acid was not influenced by the hormone. The time course, as well as the partial inhibition of the hormone effect by actinomycin D and cycloheximide, point to the hormone-induced formation of a protein which regulates phospholipase A2. The hormone did not affect the phagocytotic activity of the Kupffer cells. The quantity of [3H]arachidonic acid incorporated into phospholipids was also not altered by dexamethasone. After stimulation with zymosan, [3H]arachidonic acid was liberated from phosphatidylcholine only. Superoxide generation by rat Kupffer cells was induced by zymosan, phorbol ester and, to a much smaller extent, by platelet-activating factor. A23187 and lipopolysaccharide were without effect. In contrast to prostaglandin formation, the generation of superoxide was not influenced by dexamethasone. These results indicate that in cultured rat Kupffer cells prostaglandin formation and superoxide generation are independently triggered processes.