Phagocytosis of Leishmania donovani amastigotes is Rac1 dependent and occurs in the absence of NADPH oxidase activation

Macrophages produce little superoxide during phagocytosis of Leishmania donovani amastigotes. In this study, we characterized molecular events associated with L. donovani amastigotes uptake by mouse macrophages, to further define the mechanisms by which they are internalized without triggering superoxide production. Using transient transfections, we first showed that internalization of L. donovani amastigotes is mediated by the GTPases Rac1 and Arf6, of which Rac1 is recruited and retained on parasite-containing phagosomes. Next, we showed that, whereas internalization of amastigotes induced no superoxide release, co-internalization of serum-opsonized zymozan and amastigotes resulted in superoxide production. Furthermore, in co-internalization experiments, we detected superoxide production in over 95% of phagosomes containing IgG-opsonized SRBC compared to 5% of amastigote-harboring phagosomes. These results suggest that amastigotes evade the ability of macrophages to produce superoxide during phagocytosis. Consistently, we observed that amastigotes induced barely detectable phosphorylation of the NADPH oxidase component p47phox, leading to a defective phagosomal recruitment of p67phox and p47phox. Finally, we showed that amastigotes disrupt phagosomal lipid raft integrity, potentially interfering with NADPH oxidase assembly. Collectively, our results indicate that internalization of L. donovani amastigotes is a Rac1- and Arf6-dependent process that occurs in the absence of significant NADPH oxidase activation.     

Subcellular localization of nicotinamide adenine dinucleotide phosphate oxidase subunits in neurons and astroglia of the rat medial nucleus tractus solitarius: relationship with tyrosine hydroxylase immunoreactive neurons

Superoxide produced by the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase mediates crucial intracellular signaling cascades in the medial nucleus of the solitary tract (mNTS), a brain region populated by catecholaminergic neurons, as well as astroglia that play an important role in autonomic function. The mechanisms mediating NADPH oxidase (phagocyte oxidase) activity in the neural regulation of cardiovascular processes are incompletely understood, however the subcellular localization of superoxide produced by the enzyme is likely to be an important regulatory factor. We used immunogold electron microscopy to determine the phenotypic and subcellular localization of the NADPH oxidase subunits p47(phox), gp91(phox,) and p22(phox) in the mNTS in rats. The mNTS contains a large population of neurons that synthesize catecholamines. Significantly, catecholaminergic signaling can be modulated by redox reactions. Therefore, the relationship of NADPH oxidase subunit labeled neurons or glia with respect to catecholaminergic neurons was also determined by dual labeling for the superoxide producing enzyme and tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. In the mNTS, NADPH oxidase subunits were present primarily in somatodendritic processes and astrocytes, some of which also contained TH, or were contacted by TH-labeled axons, respectively. Immunogold quantification of NADPH oxidase subunit localization showed that p47(phox) and gp91(phox) were present on the surface membrane, as well as vesicular organelles characteristic of calcium storing smooth endoplasmic reticula in dendritic and astroglial processes. These results indicate that NADPH oxidase assembly and consequent superoxide formation are likely to occur near the plasmalemma, as well as on vesicular organelles associated with intracellular calcium storage within mNTS neurons and glia. Thus, NADPH oxidase-derived superoxide may participate in intracellular signaling pathways linked to calcium regulation in diverse mNTS cell types. Moreover, NADPH oxidase-derived superoxide in neurons and glia may directly or indirectly modulate catecholaminergic neuron activity in the mNTS.     

Phagocyte NADPH oxidase: a multicomponent enzyme essential for host defenses

Phagocytes such as neutrophils and monocytes play an essential role in host defenses against microbial pathogens. Reactive oxygen species (ROS), such as superoxide anion, hydrogen peroxide, the hydroxyl radical, and hypochlorous acid, together with microbicidal peptides and proteases, constitute their antimicrobial arsenal. The enzyme responsible for superoxide anion production and, consequently, ROS generation, is called NADPH oxidase or respiratory burst oxidase. This multicomponent enzyme system is composed of cytosolic proteins (p47phox, p67phox, p40phox, and rac1/2) and membrane proteins (p22phox and gp91phox, which form cytochrome b558) which assemble at membrane sites upon cell activation. The importance of this enzyme in host defenses is illustrated by a life-threatening genetic disorder called chronic granulomatous disease in which the phagocyte enzyme is dysfunctional, leading to life-threatening bacterial and fungal infections. Also, because ROS can damage surrounding tissues, their production, and thus NADPH oxidase activation, must be tightly regulated. This review describes the structure and activation of the neutrophil NADPH enzyme complex.     

Superoxide production in Galleria mellonella hemocytes: identification of proteins homologous to the NADPH oxidase complex of human neutrophils

The insect immune response has a number of structural and functional similarities to the innate immune response of mammals. The objective of the work presented here was to establish the mechanism by which insect hemocytes produce superoxide and to ascertain whether the proteins involved in superoxide production are similar to those involved in the NADPH oxidase-induced superoxide production in human neutrophils. Hemocytes of the greater wax moth (Galleria mellonella) were shown to be capable of phagocytosing bacterial and fungal cells. The kinetics of phagocytosis and microbial killing were similar in the insect hemocytes and human neutrophils. Superoxide production and microbial killing by both cell types were inhibited in the presence of the NADPH oxidase inhibitor diphenyleneiodonium chloride. Immunoblotting of G. mellonella hemocytes with antibodies raised against human neutrophil phox proteins revealed the presence of proteins homologous to gp91phox, p67phox, p47phox, and the GTP-binding protein rac 2. A protein equivalent to p40phox was not detected in insect hemocytes. Immunofluorescence analysis localized insect 47-kDa and 67-kDa proteins throughout the cytosol and in the perinuclear region. Hemocyte 67-kDa and 47-kDa proteins were immunoprecipitated and analyzed by matrix-assisted laser desorption ionization--time of flight analysis. The results revealed that the hemocyte 67-kDa and 47-kDa proteins contained peptides matching those of p67phox and p47phox of human neutrophils. The results presented here indicate that insect hemocytes phagocytose and kill bacterial and fungal cells by a mechanism similar to the mechanism used by human neutrophils via the production of superoxide. We identified proteins homologous to a number of proteins essential for superoxide production in human neutrophils and demonstrated that significant regions of the 67-kDa and 47-kDa insect proteins are identical to regions of the p67phox and p47phox proteins of neutrophils.     

Mechanisms of expression of NADPH oxidase components in human cultured monocytes: role of cytokines and transcriptional regulators involved

Human blood monocytes lose their capability to produce microbicidal oxidants during culture. We report that this process is associated with decreased gp91phox, p22phox and p47phox expression, release of PU.1 and CP-1 from gp91phox promoter, and PU.1 from p47phox promoter. However, in presence of IFN-gamma or TNF-alpha, the superoxide anion (O(2)(-)) production, the p47phox, gp91phox and p22phox expression, and the binding of PU.1 and CP-1 to DNA are maintained at the high levels observed in blood monocytes. To clarify the role of PU.1 in the expression of NADPH oxidase components, oligonucleotides competing for PU.1-DNA binding were added to cultured monocytes. These oligonucleotides abrogated the maintenance of gp91phox and p22phox expression by IFN-gamma and TNF-alpha, but did not inhibit the effect of these cytokines on p47phox expression and O(2)(-) production. Our results indicate that in monocytes the IFN-gamma- and TNF-alpha-induced expression of gp91phox and p22phox, but not p47phox, requires the binding of PU.1 to gp91phox promoter. However, the preservation of O(2)(-) production by IFN-gamma and TNF-alpha is unrelated to their effect on gp91phox and p22phox expression.     

The NADPH oxidase family and its inhibitors

The classical nicotinamide adenine dinucleotide phosphate (NADPH) oxidase was originally detected in neutrophils as a multicomponent enzyme that catalyzes the generation of superoxide from oxygen and the reduced form of NADPH. This enzyme is composed of two membrane-bound subunits (p22phox and gp91phox), three cytosolic subunits (p67phox, p47phox, and p40phox) and a small G-protein Rac (Rac1 and Rac2). Recently, it has been demonstrated that there are several isoforms of nonphagocytic NADPH oxidase. Endothelial cells, vascular smooth muscle cells or adventitial fibroblasts possess multiple isoforms of this enzyme. The new homologs, along with gp91phox are now designated the Nox family of NADPH oxidases and are key sources of reactive oxygen species in the vasculature. Reactive oxygen species play a significant role in regulating endothelial function and vascular tone. However, besides the participation in the processes of physiological cell, these enzymes can also be the perpetrator of oxidative stress that causes endothelial dysfunction. This review summarizes the current state of knowledge of the structure and functions of NADPH oxidase and NADPH oxidase inhibitors in the treatment of disorders with endothelial damage.     

Organ-specific and stage-dependent control of Leishmania major infection by inducible nitric oxide synthase and phagocyte NADPH oxidase

In the Leishmania major mouse model of cutaneous leishmaniasis inducible nitric oxide synthase (iNOS) is crucial for the killing of the parasite in the skin and draining lymph node. However, the effector mechanism operating against L. major in the spleen is unknown. As reactive oxygen intermediates might play a role, we analyzed macrophages and mice lacking the gp91phox subunit of the phagocyte NADPH oxidase (phox) for their ability to combat an infection with L. major. Macrophages from wild-type and gp91phox(-/-) mice had an equal capacity to kill L. major after activation by cytokines. Unlike iNOS, the activity of phox was dispensable for the resolution of the acute skin lesions and exerted only a limited effect on the containment of the parasites in the draining lymph node, but was essential for the clearance of L. major in the spleen. During the chronic phase of infection, parasites persisted at high levels in gp91phox(-/-) mice, and cutaneous lesions re-emerged in approximately 60% of these mice. gp91phox deficiency did not impair the expression of iNOS or the production of TNF and IFN-gamma. These results demonstrate that iNOS and phox are both required for the control of L. major in vivo and display unexpected organ- and stage-specific anti-leishmanial effects.     

Slc11a1-mediated resistance to Salmonella enterica serovar Typhimurium and Leishmania donovani infections does not require functional inducible nitric oxide synthase or phagocyte oxidase activity

Solute carrier family 11a member 1 (Slc11a1; formerly natural resistance-associated macrophage protein 1) encodes a late endosomal/lysosomal protein/divalent cation transporter, which regulates iron homeostasis in macrophages. During macrophage activation, Slc11a1 exerts pleiotropic effects on gene regulation and function, including generation of nitric oxide (NO) via inducible NO synthase (iNOS; encoded by Nos2A) and of reactive oxygen intermediates (ROI) via the phagocyte oxidase complex. As NO and ROI have potent antimicrobial activity in macrophages, it was assumed that their activities would contribute to Slc11a1-regulated innate resistance to Salmonella enterica serovar Typhimurium and Leishmania donovani. By intercrossing mice with gene disruptions at Nos2A and Cybb (encoding gp91phox, the heavy chain subunit of cytochrome b-245 and an essential component of phagocyte NADPH oxidase) onto equivalent Slc11a1 wild-type and mutant genetic backgrounds, we demonstrate that neither iNOS nor gp91phox activity is required for Slc11a1-mediated innate resistance to either infection. Functional gp91phox and iNOS are required to control S. enterica serovar Typhimurium in non-Slc11a1-regulated phases of infection. For L. donovani, an organ-specific requirement for iNOS to clear parasites from the spleen was observed at 50 days post-infection, but neither iNOS nor gp91phox influenced late-phase infection in the liver. This contrasted with Leishmania major infection, which caused rapid lesion growth and death in iNOS knockout mice and some exacerbation of disease with gp91phox deficiency. This highlights the adaptive differences in tissue and cellular tropisms between L. donovani and L. major and the different genes and mechanisms that regulate visceral versus cutaneous forms of the disease.     

Assembly of the phagocyte NADPH oxidase complex: chimeric constructs derived from the cytosolic components as tools for exploring structure-function relationships

Phagocytes generate superoxide (O2*-) by an enzyme complex known as reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Its catalytic component, responsible for the NADPH-driven reduction of oxygen to O2*-, is flavocytochrome b559, located in the membrane and consisting of gp91phox and p22phox subunits. NADPH oxidase activation is initiated by the translocation to the membrane of the cytosolic components p47phox, p67phox, and the GTPase Rac. Cytochrome b559 is converted to an active form by the interaction of gp91phox with p67phox, leading to a conformational change in gp91phox and the induction of electron flow. We designed a new family of NADPH oxidase activators, represented by chimeras comprising various segments of p67phox and Rac1. The prototype chimera p67phox (1-212)-Rac1 (1-192) is a potent activator in a cell-free system, also containing membrane p47phox and an anionic amphiphile. Chimeras behave like bona fide GTPases and can be prenylated, and prenylated (p67phox -Rac1) chimeras activate the oxidase in the absence of p47phox and amphiphile. Experiments involving truncations, mutagenesis, and supplementation with Rac1 demonstrated that the presence of intrachimeric bonds between the p67phox and Rac1 moieties is an absolute requirement for the ability to activate the oxidase. The presence or absence of intrachimeric bonds has a major impact on the conformation of the chimeras, as demonstrated by fluorescence resonance energy transfer, small angle X-ray scattering, and gel filtration. Based on this, a "propagated wave" model of NADPH oxidase activation is proposed in which a conformational change initiated in Rac is propagated to p67phox and from p67phox to gp91phox.     

阿托伐他汀对大鼠缺血再灌注脑组织中NADPH氧化酶源性超氧阴离子的抑制作用

目的：脑组织在缺血再灌注的早期，超氧阴离子的大量生成加重了脑组织损伤，本实验研究阿托伐他汀对缺血再灌注脑组织保护作用的可能机制。方法:成年雄性Sprague-Dawley大鼠经线栓法阻断大脑中动脉建立脑缺血再灌注模型，再灌注前经腹腔给予阿托伐他汀（立普妥）治疗。脑梗死灶体积用四唑氮蓝染色后测量；NADPH氧化酶酶活性和超氧阴离子水平使用光泽精增强化学发光法定量测定；NADPH氧化酶膜亚基gp91phox、膜易位亚基p47phox和小GTP酶Rac-1蛋白的表达用蛋白质印迹分析。结果:缺血半暗区的NADPH氧化酶活性和超氧阴离子水平增高，于再灌注2 h达到高峰，但缺血中心区的NADPH氧化酶活性和超氧阴离子水平无明显增高。阿托伐他汀预治疗能抑制再灌注2 h后缺血半暗区的NADPH氧化酶活性和超氧阴离子增高，减少膜亚基gp91phox蛋白的表达和预防细胞质亚基p47phox蛋白易位至细胞膜。结论:阿托伐他汀对缺血再灌注脑组织NADPH氧化酶源性超氧阴离子的抑制作用，是其脑保护作用机制之一。     

Oxygen radical generation and expression of NADPH oxidase genes in bottlenose dolphin (Tursiops truncatus) neutrophils

Oxygen radical generation by stimulation with phorbol myristate acetate (PMA) was evaluated in bottlenose dolphin neutrophils. A Cypridina luciferin analog-dependent chemiluminescent assay demonstrated that dolphin neutrophils generate superoxide by the addition of PMA, and that its superoxide-forming activity is completely suppressed by diphenylene iodonium, a specific inhibitor of NADPH oxidase. These results indicate that dolphin neutrophils possess NADPH oxidase activity. Furthermore, the NADPH oxidase activity (hydrogen peroxide production) in dolphin neutrophils, as well as in human neutrophils, was greater at 37 degrees C than at a lower temperature. RT-PCR with specific primers revealed that dolphin neutrophils expressed the mRNAs of the major NADPH oxidase components, which included membrane-associated flavocytochrome b (gp91(phox) and p22(phox)) and cytosolic factors (p40(phox), p47(phox), and p67(phox)), implying the existence of these protein homologues in dolphin neutrophils.     

Low energy laser light (632.8 nm) suppresses amyloid-β peptide-induced oxidative and inflammatory responses in astrocytes

Oxidative stress and inflammation are important processes in the progression of Alzheimer's disease (AD). Recent studies have implicated the role of amyloid β-peptides (Aβ) in mediating these processes. In astrocytes, oligomeric Aβ induces the assembly of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complexes resulting in its activation to produce anionic superoxide. Aβ also promotes production of pro-inflammatory factors in astrocytes. Since low energy laser has previously been reported to attenuate oxidative stress and inflammation in biological systems, the objective of this study was to examine whether this type of laser light was able to abrogate the oxidative and inflammatory responses induced by Aβ. Primary rat astrocytes were exposed to Helium-Neon laser (λ=632.8 nm), followed by the treatment with oligomeric Aβ. Primary rat astrocytes were used to measure Aβ-induced production of superoxide anions using fluorescence microscopy of dihydroethidium (DHE), assembly of NADPH oxidase subunits by the colocalization between the cytosolic p47(phox) subunit and the membrane gp91(phox) subunit using fluorescent confocal microscopy, phosphorylation of cytosolic phospholipase A(2) cPLA(2) and expressions of pro-inflammatory factors including interleukin-1β (IL-1β) and inducible nitric-oxide synthase (iNOS) using Western blot Analysis. Our data showed that laser light at 632.8 nm suppressed Aβ-induced superoxide production, colocalization between NADPH oxidase gp91(phox) and p47(phox) subunits, phosphorylation of cPLA(2,) and the expressions of IL-1β and iNOS in primary astrocytes. We demonstrated for the first time that 632.8 nm laser was capable of suppressing cellular pathways of oxidative stress and inflammatory responses critical in the pathogenesis in AD. This study should prove to provide the groundwork for further investigations for the potential use of laser therapy as a treatment for AD.     

Nox enzymes in immune cells

The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase of phagocytes is a multi-component electron transferase that uses cytoplasmic NADPH to convert molecular oxygen to superoxide anion, consequently delivering reactive oxygen species to the site of invading microorganisms. Together with soluble factors and other phagocyte-derived agents, the resultant toxic species kill and degrade the ingested microbe. Flavocytochrome b (558), a heterodimeric protein composed of gp91 phox and p22 phox, is the membrane component of the NADPH oxidase and was previously thought to be uniquely expressed in phagocytes. Based on structural homology with gp91 phox, recent studies have defined a family of NADPH oxidase proteins (Nox) that is widely distributed throughout the plant and animal kingdoms and in many tissues in multicellular organisms. The goals of this review are to review features of the phagocyte NADPH oxidase that serve as a paradigm for exploiting oxidants for host defense, and to discuss contributions of other Nox proteins to innate immunity.     

Diagnostic paradigm for evaluation of male patients with chronic granulomatous disease,based on the dihydrorhodamine 123 assay

BACKGROUND: Chronic granulomatous disease (CGD) is a phagocyte disorder caused by mutations in nicotinamide dinucleotide phosphate (NADPH) oxidase subunits. The dihydrorhodamine 123 (DHR) assay is an effective test for CGD that for most patients also might help to differentiate between the 2 most common forms, X-linked (X) gp91(phox) defect CGD and autosomal recessive (AR) p47(phox) defect CGD. However, some male patients with X-CGD have DHR patterns that overlap the AR-CGD pattern. OBJECTIVE: The purpose of this investigation was to develop a diagnostic paradigm to delineate male patients with X-CGD expressing a DHR pattern suggestive of p47(phox) deficiency. METHODS: The DHR assay measured change in fluorescence of DHR-loaded granulocytes after phorbol myristate acetate (PMA) stimulation. Western blot analysis measured the presence of NADPH oxidase subunits gp91(phox), p47(phox), p67(phox), and p22(phox). CYBB exonic sequencing was performed on PCR-amplified genomic DNA through use of intronic flanking primers. Ferricytochrome-c assay evaluated specific superoxide production by PMA-stimulated granulocytes. RESULTS: Although 83% of patients with X-CGD have virtually no neutrophil DHR activity, we found that 17% of patients, proven to have X-CGD by other criteria, have modest DHR activity that is most consistent with p47(phox) deficiency. We describe a diagnostic paradigm to deal with such patients, and we present 2 cases, along with results of additional studies, including carrier evaluation, protein assessment, and mutation analysis, that are useful in establishing the genotype under these circumstances. DHR assays from the 2 patients described showed a fluorescence shift most characteristic of p47(phox)-AR-CGD; however, each of the patients' mothers showed mosaicism with a bimodal DHR pattern. Patient 1 had some gp91(phox) protein with a Y41D mutation and modest superoxide activity. Patient 2 had a normal level of gp91(phox) protein with a C537R mutation without detectable superoxide activity, as determined by ferricytochrome-c assay, despite the modest DHR activity. CONCLUSIONS: Evaluation of male patients with CGD with modest DHR activity should initially include evaluation of potential female carriers for mosaicism with the use of the DHR assay. In circumstances in which this is uninformative, patients should be referred to centers capable of additional testing, including Western blot analysis and CYBB mutation analysis, to clarify the disease genotype.     

Chronic granulomatous disease: more than the lack of superoxide?

Chronic granulomatous disease (CGD) is an inherited disease characterized by severe and recurrent bacterial and fungal infections manifested in most cases in early childhood. Phagocytic cells of CGD patients are unable to produce superoxide anions, and their efficiency in bacterial killing is significantly impaired. Recent work has shown alterations in the electrophysiological properties of CGD granulocytes, which might contribute to the pathogenesis of the disease. The new aspects that we discuss in this review concern the proton channel function of gp91phox (the electron-transporting subunit of the NADPH oxidase) and the electrogenic activity of the active enzyme complex, which can affect the transmembrane trafficking of several ions. Based on the reviewed data, we also propose a hypothesis that the absence of a functional NADPH oxidase in CGD neutrophils could result in altered ion compositions within intracellular and intraphagosomal spaces during the process of phagocytosis.     

The search for a genetic defect in Polish patients with chronic granulomatous disease

INTRODUCTION: Chronic granulomatous disease (CGD)is a rare inherited disorder in which phagocytic cells are unable to generate superoxide anions.Patients with CGD are predisposed to recurrent bacterial and fungal infections because the superoxide-generating NADPH oxidase activity is needed for efficient killing of microbes.Among the at least 5 subunits cre-ating a functional NADPH oxidase, a molecular defect located in any of the gp91phox, p22phox, p47phox, or p67phox subunits may cause CGD. MATERIAL/METHODS: In this study,8 patients were diagnosed with CGD on the basis of clinical findings and absence of nitroblue tetrazolium reduction in phagocytes. Southern blot analysis, GeneScan, and direct sequencing were performed to define particular DNA mutations. RESULTS: Among 6 X-linked CGD (X-CGD)patients, 4 different mutations were identified in the X-linked CYBB gene (encoding gp91phox)by direct sequencing. A novel missense mutation, located in the NADPH-binding region of gp91phox,was found in 2 brothers. One frameshift 1578delA, one splicing 252G->A mutation, and one partial gene deletion were also identified. The molecular defect in the NCF1 gene (encoding p47phox)was established in 2 patients. One was DeltaGT/DeltaGT homozygote, the other carried, besides this GT deletion on one allele, a unique Phe118stop mutation on the other. CONCLUSIONS: In general, the X-CGD patients within the group followed a more severe clinical course than the patients with an NCF1 defect. However, the lack of a straightforward genotype phenotype correlation indicates that the clinical severity of CGD depends also on other antimicrobial host-defense systems.     

Evaluation of the expression of NADPH oxidase components during maturation of HL-60 cells to neutrophil lineage

To understand the expression of NADPH oxidase components during neutrophil maturation, we examined the expression of mRNAs and proteins for NADPH oxidase components, and the superoxide-producing activity using HL-60 cells incubated with dimethyl sulfoxide (DMSO). Northern blot and Western blot analyses revealed that gp91(phox), p67(phox), and p47(phox) were expressed after myelocyte stages, whereas p22(phox), p40(phox), and rac-2 were expressed from the promyelocyte stage. Furthermore, immunocytochemical staining of DMSO-induced HL-60 cells indicated that gp91(phox), p67(phox), and p47(phox) were detected only after myelocyte stages (myelocytes, metamyelocytes, band cells, and segmented cells), whereas p22(phox), p40(phox), and rac-2 were detected from the promyelocyte stage. In addition, nitro blue tetrazolium (NBT) assay showed that superoxide could be produced after myelocyte stages but not produced before promyelocyte stages. Moreover, almost the same results as those with DMSO-induced HL-60 cells were obtained using human bone-marrow cells by immunocytochemical staining and NBT assay, except that p22(phox) was detected by immunocytochemical staining after myelocyte stages in bone-marrow cells. Together, these observations indicate that all the components for NADPH oxidase are expressed, and the superoxide-producing activity is obtained after myelocyte stages during neutrophil maturation.