Antineutrophil cytoplasm antibody-induced neutrophil nitric oxide production is nitric oxide synthase independent

Cardiovascular bioimaging of nitric oxide: Achievements, challenges, and the future

Nitric oxide (NO) is a ubiquitous, volatile, cellular signaling molecule that operates across a wide physiological concentration range (pM-µM) in different tissues. It is a highly diffusible messenger and intermediate in various metabolic pathways. NO plays a pivotal role in maintaining optimum cardiovascular function, particularly by regulating vascular tone and blood flow. This review highlights the need for accurate, real-time bioimaging of NO in clinical diagnostic, therapeutic, monitoring, and theranostic applications within the cardiovascular system. We summarize electrochemical, optical, and nanoscale sensors that allow measurement and imaging of NO, both directly and indirectly via surrogate measurements. The physical properties of NO render it difficult to accurately measure in tissues using direct methods. There are also significant limitations associated with the NO metabolites used as surrogates to indirectly estimate NO levels. All these factors added to significant variability in the measurement of NO using available methodology have led to a lack of sensors and imaging techniques of clinical applicability in relevant vascular pathologies such as atherosclerosis and ischemic heart disease. Challenges in applying current methods to biomedical and clinical translational research, including the wide physiological range of NO and limitations due to the characteristics and toxicity of the sensors are discussed, as are potential targets and modifications for future studies. The development of biocompatible nanoscale sensors for use in combination with existing clinical imaging modalities provides a feasible opportunity for bioimaging NO within the cardiovascular system.

Nitric oxide metabolism is impaired by type 1 diabetes and diabetic nephropathy

Diabetes leads to reduced nitric oxide bioavailability, resulting in endothelial dysfunction. However, overproduction of nitric oxide due to hyperglycaemia is associated with oxidative stress and tissue damage. The objective of this study was to characterise nitric oxide production (NO) and added nitrite and nitrate (NO₂ ^-+NO₃ ^-) concentration in the blood and urine of patients with and without diabetic nephropathy. A total of 268 patients with type 1 diabetes and 69 healthy subjects were included. Diabetic nephropathy was defined as macroalbuminuria and/or estimated glomerular filtration rate below 60 ml/min/1.73 cm². NO₂ ^-+NO₃ ^- concentration was measured by Griess reaction. Production of NO was detected by electron paramagnetic resonance spectroscopy. Blood NO was demonstrated to be higher (P<0.001) and serum NO₂ ^-+NO₃ ^- was lower (P=0.003) in patients with type 1 diabetes and no nephropathy vs. healthy subjects. However, serum NO₂ ^-+NO₃ ^- concentration in patients with diabetes and nephropathy did not differ from the levels observed in healthy controls. Urine excretion of NO₂ ^-+NO₃ ^- was significantly decreased in patients with nephropathy, compared with patients without diabetic kidney disease (P=0.006) and healthy subjects (P=0.010). A significant positive correlation was observed between urine NO₂ ^-+NO₃ ^- and estimated glomerular filtration rate in patients with type 1 diabetes (P=0.002) and healthy subjects (P=0.008). Estimated glomerular filtration rate, albuminuria and diabetic nephropathy status were significant predictors of the whole blood NO and NO₂ ^-+NO₃ ^- in serum and urine in patients with type 1 diabetes, as identified by linear regression models. The present study concludes that NO metabolism is impaired by type 1 diabetes and diabetic nephropathy.

Complement Factor H Inhibits Anti-Neutrophil Cytoplasmic Autoantibody-Induced Neutrophil Activation by Interacting With Neutrophils

Our previous study demonstrated that plasma levels of complement factor H (FH) were inversely associated with the disease activity of patients with anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV). In addition to serving as an inhibitor of the alternative complement pathway, there is increasing evidence demonstrating direct regulatory roles of FH on several cell types. Here, we investigated the role of FH in the process of ANCA-mediated activation of neutrophils and neutrophil–endothelium interaction. We demonstrated that FH bound to neutrophils by immunostaining and flow cytometry. Interestingly, ANCA-induced activation of neutrophils, including respiratory burst and degranulation, was inhibited by FH. Although FH enhanced neutrophils adhesion and migration toward human glomerular endothelial cells (hGEnCs), it inhibited ANCA-induced activation of neutrophils in the coculture system of hGEnCs and neutrophils. Moreover, the activation and injury of hGEnCs, reflected by the level of endothelin-1 in the supernatant of cocultures, was markedly reduced by FH. However, we found that FH from patients with active AAV exhibited a deficient ability in binding neutrophils and inhibiting ANCA-induced neutrophil activation in fluid phase and on endothelial cells, as compared with that from healthy controls. Therefore, our findings indicate a novel role of FH in inhibiting ANCA-induced neutrophil activation and protecting against glomerular endothelial injury. However, FH from patients with active AAV are deficient in their ability to bind neutrophils and inhibit neutrophil activation by ANCA. It further extends the current understanding of the pathogenesis of AAV, thus providing potential clues for intervention strategies.

Effects of phosphodiester and phosphorothioate ODN2216 on leukotriene synthesis in human neutrophils and neutrophil apoptosis

Polymorphonuclear leukocytes (PMNLs, neutrophils) play a major role in the initiation and resolution of the inflammatory response, and neutrophil apoptosis is a critical step in resolving inflammation. We examined the effects of oligodeoxynucleotide (ODN) species with different numbers of phosphodiester and phosphorothioate bonds on leukotriene synthesis in PMNLs and on neutrophil apoptosis. Our modifications were based on the well-known ODN2216 molecule (Krug et al., 2001). Treatment of cultured human neutrophils with ODN2216 accelerated apoptosis except in the case of a species with only phosphodiester bonds. The ODNs with poly(g) (phosphorothioate) sequences at both ends and a phosphodiester inner core had maximal effects on leukotriene synthesis in neutrophils and inhibited formation of 5-lipoxygenase metabolites. Addition of phosphodiester and phosphorothioate ODNs to PMNLs produced distinct effects on superoxide and nitric oxide formation: phosphorothioate-containing ODNs concomitantly stimulated production of nitric oxide and superoxide, which may rapidly combine to generate peroxynitrite. Altogether, our results describe strong activation of neutrophil's cellular responses by phosphorothioate ODN2216. We propose that phosphorothioate modification of ODNs represents a potential mechanism of PMNL activation.

Myeloperoxidase: a front-line defender against phagocytosed microorganisms

Successful immune defense requires integration of multiple effector systems to match the diverse virulence properties that members of the microbial world might express as they initiate and promote infection. Human neutrophils--the first cellular responders to invading microbes--exert most of their antimicrobial activity in phagosomes, specialized membrane-bound intracellular compartments formed by ingestion of microorganisms. The toxins generated de novo by the phagocyte NADPH oxidase and delivered by fusion of neutrophil granules with nascent phagosomes create conditions that kill and degrade ingested microbes. Antimicrobial activity reflects multiple and complex synergies among the phagosomal contents, and optimal action relies on oxidants generated in the presence of MPO. The absence of life-threatening infectious complications in individuals with MPO deficiency is frequently offered as evidence that the MPO oxidant system is ancillary rather than essential for neutrophil-mediated antimicrobial activity. However, that argument fails to consider observations from humans and KO mice that demonstrate that microbial killing by MPO-deficient cells is less efficient than that of normal neutrophils. We present evidence in support of MPO as a major arm of oxidative killing by neutrophils and propose that the essential contribution of MPO to normal innate host defense is manifest only when exposure to pathogens overwhelms the capacity of other host defense mechanisms.

Meta-analysis of myeloperoxidase G-463/A polymorphism in anti-neutrophil cytoplasmic autoantibody-positive vasculitis

Wegener's granulomatosis, microscopic polyangiitis and Churg Strauss syndrome are small-vessel vasculitides associated with anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) and myeloperoxidase (MPO). A G to A polymorphism at position 463 in the promoter region of the MPO gene, which leads to the loss of a SP1 transcription binding site in an Alu hormone responsive element, reduces MPO expression. We hypothesized that MPO alleles may play a role in determining disease susceptibility or severity in ANCA-associated vasculitis (AASV). MPO genotypes were determined by restriction fragment length polymorphism polymerase chain reaction (RFLP/PCR) in 134 Caucasian patients (Wegener's granulomatosis, n = 69; microscopic polyangiitis, n = 65; PR3-ANCA n = 91; MPO-ANCA, n = 43) and 150 matched healthy controls. There was no difference in survival to renal failure or death in patients with the different MPO alleles (chi(2) = 0.904, P = 0.6362) or in presenting serum creatinine concentration based on MPO genotype (chi(2) = 0.389, P = 0.8232). There was no significant difference in genotype frequencies between controls (13AA, 102GG, 35GA) and patients (14AA, 97GG, 23GA: chi(2) = 1.75, P = 0.417), patients with Wegener's granulomatosis (5AA, 53GG, 11GA: chi(2) = 1.864, P = 0.3938) or patients with microscopic polyangiitis (9AA, 44GG, 12GA: chi(2) = 1.682, P = 0.4317). A meta-analysis of our study and two previous studies showed that there was no association between the myeloperoxidase G-463/A polymorphism and the risk of developing ANCA-associated vasculitis; GG versus GA plus AA (odds ratio 1.14; 95% confidence interval 0.86-1.50). The MPO G-463/A polymorphism is not a risk factor for the development or severity of AASV.

Chimeric antibodies to proteinase 3 of IgG1 and IgG3 subclasses induce different magnitudes of functional responses in neutrophils

BACKGROUND

Antineutrophil cytoplasmic antibodies (ANCA) are associated with small-vessel vasculitis and have been implicated in its pathogenesis. The subclass distribution of ANCA IgG deviates from normal patterns, and it has been suggested that the IgG3 subclass may have pathogenic potential over the IgG1 subclass and may be more likely to be associated with active disease and renal involvement.

OBJECTIVE

To deal with potential pathogenicity, chimeric antibodies were constructed of IgG1 and three subclasses with human IgG1 or three constant regions and a murine-derived variable region that binds an epitope within the ANCA antigen proteinase 3 (PR3) that is recognised by human autoantibodies.

METHODS

The antibodies were characterised for binding to PR3, including affinity and avidity, before being used as tools to explore their ability to activate human neutrophils for superoxide release, cytokine release, degranulation and ability to induce neutrophil adhesion under flow.

RESULTS

Both subclass antibodies elicited similar neutrophil responses for superoxide release, degranulation and interleukin (IL) 8 production, although quantitative responses showed that the IgG1 subclass favoured degranulation and the IgG3 subclass favoured IL8 production. Both antibodies were able to convert neutrophils from selectin-dependent rolling adhesion to integrin-dependent stationary adhesion in a flow assay.

CONCLUSIONS

These findings indicate that humanised antibodies directed against a single epitope of PR3 can recapitulate the effects of polyclonal human ANCA, which recognises multiple PR3 epitopes. Further, PR3-ANCA of both IgG1 and IgG3 subclasses can activate neutrophils, although the more potent IL8 response by IgG3 PR3-ANCA may encourage further neutrophil recruitment and amplify injury.

Anti-Neutrophil Cytoplasmic Autoantibodies: A Renewed Paradigm in Periodontal Disease Pathogenesis?

In the past, various models including the autoimmunity model have been proposed to explain the pathogenesis of periodontal diseases. The aim of this review is to introduce the pathogenic role of anti-neutrophil cytoplasmic autoantibodies (ANCAs) in various autoimmune diseases and compare these conditions with periodontal disease to elucidate common pathogenic mechanisms. Also, a novel model to explain the pathogenesis of periodontal disease based on the concept of ANCA-associated autoimmunity is proposed. This encompasses a wide array of biochemical mediators that range from direct and indirect initiators of ANCA production and eventual release of proinflammatory mediators and free radicals, all of which have been implicated in periodontal tissue destruction in the past. In addition, specific links between the typical ANCA-associated diseases and periodontal disease are discussed. Finally, a new paradigm in the periodontal disease-associated destruction is proposed that includes the currently accepted mechanism, namely, the genetic-microbial-host interactions.

The role of neutrophils in the induction of glomerulonephritis by anti-myeloperoxidase antibodies

In humans, circulating anti-neutrophil cytoplasm autoantibodies (ANCAs) with specificity for myeloperoxidase (MPO) are strongly associated with the development of pauci-immune necrotizing and crescentic glomerulonephritis (NCGN). In mice, we have demonstrated that intravenous injection of mouse antibodies specific for mouse MPO induces NCGN that closely mimics the human disease. We now report that the development of NCGN in this experimental model is accompanied by glomerular accumulation of neutrophils and macrophages. Neutrophil infiltration was most conspicuous at sites of glomerular necrosis and crescent formation, with macrophages also most numerous in crescents. Lymphocytes, however, were sparse in acute lesions. Importantly, mice that were depleted of circulating neutrophils with NIMP-R14 rat monoclonal antibodies were completely protected from anti-MPO IgG-induced NCGN. These findings provide direct evidence that neutrophils play a major role in the pathogenesis of anti-MPO-induced NCGN in this animal model and implicate neutrophils in the induction of human ANCA disease. This raises the possibility that therapeutic strategies to reduce circulating neutrophils could be beneficial to patients with ANCA-induced NCGN.

Endothelial cells, antineutrophil cytoplasmic antibodies, and cytokines in the pathogenesis of systemic vasculitis

Endothelial cells play a pivotal role in the pathogenesis of systemic vasculitis. Endothelial cells have significant proinflammatory activities, amplifying and perpetuating the inflammatory process and contributing to vessel regeneration and repair. Significant contributions have improved the understanding of additional ways through which antineutrophil cytoplasmic antibodies (ANCA) may potentiate neutrophil- and monocyte-mediated endothelial cell activation and damage. Signaling pathways mediating ANCA effects have been delineated, and new animal models have demonstrated the pathogenic role of ANCA in the development of systemic vasculitis. Significant efforts have identified anti-endothelial cell antibody specificities and elucidated mechanisms through which these antibodies may promote endothelial cell activation and injury. New ways to assess in vivo endothelial cell damage and dysfunction also have been developed. In addition, besides being a relevant compensatory mechanism for ischemia, angiogenesis may have important proinflammatory functions in vasculitis. The potential relevance of bone-marrow-derived endothelial cell precursors in neovascularization has begun to be appreciated.

Pathogenesis of diseases associated with antineutrophil cytoplasm autoantibodies

Little is known about the etiologies of diseases associated with circulating antineutrophil cytoplasm autoantibodies (ANCA), such as primary vasculitides and inflammatory bowel diseases. However, the understanding of immune mechanisms supposedly involved in the pathogenesis of these diseases is still growing. In the present review, we first focus on the mechanisms triggering the development of ANCA, including the potential role of microbial superantigens and the possible defect(s) in the progression of apoptosis or in the removal of apoptotic cells. We next concentrate on the contribution of ANCA to the clinical symptoms and on the pathogenic role of ANCA, including the accessibility of ANCA antigens as targets for circulating antibodies and the mode of action of ANCA. Mechanisms of neutrophil activation by ANCA include the engagement of Fcgamma receptors, the possible mechanisms of neutrophil-mediated tissue damage, and the neutrophil-endothelial interaction.

Suppressive activity of macrolide antibiotics on nitric oxide production from nasal polyp fibroblasts in vitro

The influence of macrolide antibiotics on nitric oxide (NO) generation was examined using human nasal polyp fibroblasts (NPFs) in vitro. Addition of roxithromycin (RXM) at a concentration of > 7.5 microg/ml to cell cultures was shown to suppress NO production in response to stimulation with 25.0 ng/ml tumor necrosis factor (TNF)-alpha. However, jyosamycin (JM) did not suppress NO production from NPFs induced by TNF-alpha stimulation in vitro, even when added to cell cultures at a concentration of 20.0 microg/ml. We then examined the influence of RXM on inducible nitric oxide synthase (iNOS) mRNA expression in NPFs. Addition of RXM at a dose of 7.5 microg/ml to cell cultures caused reduction of iNOS mRNA expression, which was enhanced by TNF-alpha stimulation in vitro.

Myeloperoxidase in kidney disease

In glomerular and tubulointerstitial disease, polymorphonuclear- and monocyte-derived reactive oxygen species may contribute to oxidative modification of proteins, lipids, and nucleic acids. In part, the processes instigated by reactive oxygen species parallel events that lead to the development of atherosclerosis. Myeloperoxidase (MPO), a heme protein and catalyst for (lipo)protein oxidation is present in these mononuclear cells. The ability of MPO to generate hypochlorous acid/hypochlorite (HOCl/OCl-) from hydrogen peroxide in the presence of chloride ions is a unique and defining activity for this enzyme. The MPO-hydrogen peroxide-chloride system leads to a variety of chlorinated protein and lipid adducts that in turn may cause dysfunction of cells in different compartments of the kidney. The aim of this article is to cover and interpret some experimental and clinical aspects in glomerular and tubulointerstitial diseases in which the MPO-hydrogen peroxide-chloride system has been considered an important pathophysiologic factor in the progression but also the attenuation of experimental renal disease. The colocalization of MPO and HOCl-modified proteins in glomerular peripheral basement membranes and podocytes in human membranous glomerulonephritis, the presence of HOCl-modified proteins in mononuclear cells of the interstitium and in damaged human tubular epithelia, the inflammation induced and exacerbated by MPO antibody complexes in necrotizing glomerulonephritis, and the presence of HOCl-modified epitopes in urine following hyperlipidemia-induced renal damage in rodents suggest that MPO is an important pathogenic factor in glomerular and tubulointerstitial diseases. Specifically, the interaction of MPO with nitric oxide metabolism adds to the complexity of actions of oxidants and may help to explain bimodal partly detrimental partly beneficial effects of the MPO-hydrogen peroxide-chloride system in redox-modulated renal diseases.

Up-regulation of inducible nitric oxide synthase and nitric oxide in Helicobacter pylori-infected human gastric epithelial cells: possible role of interferon-gamma in polarized nitric oxide secretion

BACKGROUND

Nitric oxide (NO) generated by nitric oxide synthase (NOS) is known to be an important modulator of the mucosal inflammatory response. In this study, we questioned whether Helicobacter pylori infection could up-regulate the epithelial cell inducible NOS (iNOS) gene expression and whether NO production could show polarity that can be regulated by immune mediators.

MATERIALS AND METHODS

Human gastric epithelial cell lines were infected with H. pylori, and the iNOS mRNA expression was assessed by quantitative RT-PCR. NO production was assayed by determining nitrite/nitrate levels in culture supernatants. To determine the polarity of NO secretion by the H. pylori-infected epithelial cells, Caco-2 cells were cultured as polarized monolayers in transwell chambers, and NO production was measured.

RESULTS

iNOS mRNA levels were significantly up-regulated in the cells infected with H. pylori, and expression of iNOS protein was confirmed by Western blot analysis. Increased NO production in the gastric epithelial cells was seen as early as 18 hours postinfection, and reached maximal levels by 24 hours postinfection. The specific MAP kinase inhibitors decreased H. pylori-induced iNOS and NO up-regulation. After H. pylori infection of polarized epithelial cells, NO was released predominantly into the apical compartment, and IL-8 was released predominantly into basolateral compartment. The addition of IFN-gamma to H. pylori-infected polarized epithelial cells showed a synergistically higher apical and basolateral NO release.

CONCLUSION

These results suggest that apical NO production mediated by MAP kinase in H. pylori-infected gastric epithelial cells may influence the bacteria and basolateral production of NO and IL-8 may play a role in the tissue inflammation.

New findings in pathogenesis of antineutrophil cytoplasm antibody-associated vasculitis

There has been a profusion of studies related to the pathogenesis of antineutrophil cytoplasm antibody-associated small vessel vasculitis. Further definition of epitopes on the major antigens, proteinase-3 and myeloperoxidase, has been sought, and intracellular signal transduction pathways after antineutrophil cytoplasm antibody-neutrophil interactions are beginning to be explored. Antineutrophil cytoplasm antibody stimulation of neutrophils has highlighted the functional importance of the accelerated death that follows the initial activation. The consequences of neutrophil and monocyte activation for endothelium and tissue damage continue to point toward an inflammatory process that has become dysregulated. Factors that initiate vasculitis are being identified slowly. The most secure identifiable environmental trigger is the antithyroid drug propylthiouracil. It is likely that environmental factors operate against a background genetic susceptibility, and polymorphisms in genes for proteins associated with inflammation are being tested for possible links with small vessel vasculitides.

Leukocyte-endothelial interactions in antineutrophil cytoplasmic antibody-associated systemic vasculitis

The etiology of ANCA-associated vasculitis is unknown. Currently, it is believed that disease may be triggered by infection with the release of proinflammatory cytokines in genetically susceptible individuals. Priming of PMNs and endothelial cells by these cytokines allows ANCAs to activate PMNs, with damage localized to the endothelium, resulting in early lesions. Damage and activation of endothelial cells produces proinflammatory chemokines and cytokines with influxes of monocytes and T cells that intensify endothelial damage. In the kidney, these changes eventually lead to crescent formation. Antigen-specific memory T cells persist after disease remission with the potential of reactivation and disease relapse. Although our understanding of the pathophysiologic mechanisms of ANCA-associated vasculitis is far greater now than when ANCAs were first identified in 1982, more experimental work in combination with clinical observations is required to further elucidate these mechanisms.