Nitric Oxide Derived from Human Umbilical Vein Endothelial Cells Inhibits Transendothelial Migration of Neutrophils

A Novel Ruthenium-based Molecular Sensor to Detect Endothelial Nitric Oxide

Nitric oxide (NO) is a key regulator of endothelial cell and vascular function. The direct measurement of NO is challenging due to its short half-life, and as such surrogate measurements are typically used to approximate its relative concentrations. Here we demonstrate that ruthenium-based [Ru(bpy)₂(dabpy)]²⁺ is a potent sensor for NO in its irreversible, NO-bound active form, [Ru(bpy)₂(T-bpy)]²⁺. Using spectrophotometry we established the sensor’s ability to detect and measure soluble NO in a concentration-dependent manner in cell-free media. Endothelial cells cultured with acetylcholine or hydrogen peroxide to induce endogenous NO production showed modest increases of 7.3 ± 7.1% and 36.3 ± 25.0% respectively in fluorescence signal from baseline state, while addition of exogenous NO increased their fluorescence by 5.2-fold. The changes in fluorescence signal were proportionate and comparable against conventional NO assays. Rabbit blood samples immediately exposed to [Ru(bpy)₂(dabpy)]²⁺ displayed 8-fold higher mean fluorescence, relative to blood without sensor. Approximately 14% of the observed signal was NO/NO adduct-specific. Optimal readings were obtained when sensor was added to freshly collected blood, remaining stable during subsequent freeze-thaw cycles. Clinical studies are now required to test the utility of [Ru(bpy)₂(dabpy)]²⁺ as a sensor to detect changes in NO from human blood samples in cardiovascular health and disease.

Neutrophil's weapons in atherosclerosis

Neutrophils are important components of immunity associated with inflammatory responses against a broad spectrum of pathogens. These cells could be rapidly activated by proinflammatory stimuli and migrate to the inflamed and infected sites where they release a variety of cytotoxic molecules with antimicrobial activity. Neutrophil antibacterial factors include extracellular proteases, redox enzymes, antimicrobial peptides, and small bioactive molecules. In resting neutrophils, these factors are stored in granules and released upon activation during degranulation. These factors could be also secreted in a neutrophil-derived microparticle-dependent fashion. Neutrophils exhibit a unique property to produce neutrophil extracellular traps (NETs) composed of decondensed chromatin and granular proteins to catch and kill bacteria. Neutrophil-released factors are efficient in inactivation and elimination of pathogens through oxidation-dependent or independent damage of bacterial cells, inactivation and neutralization of virulence factors and other mechanisms. However, in chronic atherosclerosis-associated inflammation, protective function of neutrophils could be impaired and misdirected against own cells. This could lead to deleterious effects and progressive vascular injury. In atherogenesis, a pathogenic role of neutrophils could be especially seen in early stages associated with endothelial dysfunction and induction of vascular inflammation and in late atherosclerosis associated with plaque rupture and atherothrombosis. Assuming a prominent impact of neutrophils in cardiovascular pathology, developing therapeutic strategies targeting neutrophil-specific antigens could have a promising clinical potential.

Enhanced generation of reactive oxygen species by interferon-γ may have contributed to successful treatment of invasive pulmonary aspergillosis in a patient with chronic granulomatous disease

Invasive pulmonary aspergillosis (IPA) is a life-threatening complication of chronic granulomatous disease (CGD), a rare inherited disorder of phagocytes that is characterized by a defect in the production of reactive oxygen species (ROS) caused by mutations in NADPH oxidase 2. Here, we report a case of successful treatment of IPA complicated with CGD by the administration of interferon-γ (IFN-γ) in combination with voriconazole. The patient carried a splice site mutation in the CYBB gene, and the neutrophils could produce a certain amount of ROS. In this case, augmentation of ROS generation in the patient's neutrophils was observed after in vivo IFN-γ treatment, which may be attributable to the induction of a normal CYBB gene in the myeloid progenitor cells. This treatment, in combination with voriconazole, may have contributed to the reversal of IPA in this patient. These results suggest that the in vivo use of IFN-γ may augment ROS generation in CGD neutrophils, thus leading to the successful treatment of severe IPA.

Inhibition of nitric oxide synthesis enhances leukocyte rolling and adhesion in human microvasculature

Background

Nitric oxide (NO) is a multifunctional signaling molecule that regulates important cellular events in inflammation including leukocyte recruitment. Previous studies have shown that pharmacological inhibition of NO synthesis induces leukocyte recruitment in various in vitro and animal models. However, it is not known whether NO modulation has similar effects on leukocyte-endothelial cell interactions within the human microvasculature. The present study explored the effect of systemic L-NAME treatment on leukocyte recruitment in the SCID-hu mouse model.

Methods

Human skin xenografts were transplanted in SCID mice to study human leukocyte dynamics in human vasculature. Early events of human leukocyte recruitment in human vasculature were studied using intravital microscopy. NO synthesis was pharmacologically inhibited using N^G-nitro-L-arginine methyl ester (L-NAME). Immunohistochemical analysis was performed to elucidate E-selectin expression in human xenograft skin. Human neutrophil-endothelial cell interactions were also studied in an in vitro flow chamber assay system. P- and E-selectin expression on cultured human umbilical vein endothelial cells (HUVECs) was measured using ELISA. Platelet-activating factor (PAF) synthesis was detected using a TLC-based assay.

Results

L-NAME treatment significantly enhanced the rolling and adhesion of human leukocytes to the human vasculature. Functional blocking of P- and E-selectins significantly inhibited rolling but not adhesion induced by inhibition of NO synthesis. Systemic L-NAME treatment enhanced E-selectin expression in human xenograft skin. L-NAME treatment significantly enhanced P- and E-selectin expression on HUVECs. L-NAME treatment did not significantly modify neutrophil rolling or adhesion to HUVECs indicating that L-NAME−induced subtle P- and E-selectin expression was insufficient to elicit dynamic neutrophil-HUVEC interactions in vitro. Moreover, synthesis of endothelial-derived PAF was not significantly modified by L-NAME treatment. These results point to the accelerated leukocyte recruitment in human vasculature following suppression of NO synthesis, effects that are mediated by P- and E-selectins. The findings are, however, not supported by the in vitro data.

Conclusion

Inhibition of endogenous NO triggers early events of human leukocyte recruitment in human vasculature, involving complex cellular or molecular mechanisms in addition to P- and E-selectin-mediated leukocyte rolling.

Human cord blood mononuclear cells decrease cytokines and inflammatory cells in acute myocardial infarction

We investigated whether human umbilical cord blood mononuclear cells (HUCBC), which contain hematopoietic and mesenchymal progenitor cells, can limit myocardial cytokine expression and inflammatory cell infiltration in acute myocardial infarction. We permanently ligated the left coronary artery of rats and injected into the myocardium either Isolyte or 4 x 10(6) HUCBC in Isolyte and measured myocardial cytokines with antibody arrays at 2, 6, 12, 24, and 72 hours after infarction. We then measured with flow cytometry myocardial macrophages, neutrophils and lymphocytes at 12, 24, and 72 hours after infarctions in rats treated with either intramyocardial Isolyte or 4 x 10(6) HUCBC. In the Isolyte-treated hearts, between 2 and 12 hours after myocardial infarction, tumor necrosis factor-alpha increased from 6.7 +/- 0.9% to 52.3 +/- 4.7%, monocyte chemoattract protein increased from 9.5 +/- 1.2% to 39.8 +/- 2.1%, fractalkine increased from 11 +/- 1.5% to 28.1 +/- 1.3%, ciliary neurotrophic factor increased from 12.1 +/- 0.02% to 25.9 +/- 1.1%, macrophage inflammatory protein increased from 10.3 +/- 1.5% to 23.9.0 +/- 1.4%, interferon-gamma increased from 8.7 +/- 0.4% to 26.0 +/- 1.6%, interleukin-1beta increased from 6.1 +/- 0.04% to 19.0 +/- 1.2%, and IL-4 increased from 5.9 +/- 0.03% to 15 +/- 1.5% (all p < 0.001 compared with controls). The concentrations of fractalkine remained significantly increased at 72 hours after acute infarction. In contrast, the myocardial concentrations of these cytokines did not significantly change in HUCBC treated hearts at 2, 6, 12, 24, or 72 hours after infarction. The percentage of neutrophils increased from 0.04 +/- 0.2%/50,000 heart cells in the controls to 5.3 +/- 1.2%/50,000 heart cells 12 hours after infarction in Isolyte-treated hearts but averaged only 1.3 +/- 0.7%/50,000 heart cells in HUCBC treated hearts (p < 0.02). Thereafter, the percentages of neutrophils rapidly decreased at 24 and at 72 hours after infarction and averaged 0.6 +/- 0.2%/50,000 heart cells at 72 hours after infarction in Isolyte-treated hearts in contrast to 0.2 +/- 0.1%/50,000 cells in HUCBC hearts (p < 0.05). Moreover, the percentages of neutrophils at 24 and 72 hours in HUCBC hearts were not significantly different from controls. At 24 hours post infarction, the percentage of CD3 and CD4 lymphocytes were 10.7 +/- 1.4% and 6.3 +/- 1.1%/50,000 cells in Isolyte hearts in comparison with only 4.9 +/- 0.8% and 2.9 +/- 0.5% in HUCBC hearts (p < 0.005 for Isolyte versus HUCBC). The percentage of CD11b macrophages was 2.8 +/- 0.3% in Isolyte hearts and 1.9 +/- 0.2% in HUCBC treated hearts (p < 0.05). At 72 hours after infarction, the percentage of CD3 and CD4 lymphocytes averaged 8.0 +/- 1.1% and 5.1 +/- 0.8%/50,000 heart cells in Isolyte hearts in comparison with only 4.1 +/- 0.5% and 2.3 +/- 0.4%/50,000 heart cells in the HUCBC treated infarctions (p < 0.005). Left ventricular infarct sizes in Isolyte-treated hearts at 72 hours post infarction averaged 15.7 +/- 1.4% of the left ventricular muscle area in contrast to HUCBC treated infarctions that averaged 6.9 +/- 1.4% of the left ventricular muscle area (p < 0.02). Moreover in rats followed for 2 months post infarction, the LV ejection fractions decreased to 65.4 +/- 1.9% and 69.1 +/- 1.9% at 1 and 2 months after infarction in Isolyte-treated hearts and were significantly different from HUCBC treated hearts that averaged 72.1 +/- 1.3% and 75.7 +/- 1.4% (both p < 0.02). The present experiments suggest that an important mechanism whereby HUCBC limit infarct size and improve left ventricular ejection fraction is by significantly limiting inflammatory cytokines and inflammatory cells in infarcted myocardium.

Regulation of endothelial barrier function by reactive oxygen and nitrogen species

Excessive generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), by activated neutrophils and endothelial cells, has been implicated in the pathophysiology of endothelial barrier dysfunction. Disruption of the integrity of this barrier markedly increases permeability to fluids, solutes and inflammatory cells and is the hallmark of many disorders such as acute lung injury (ALI) and sepsis. There has been considerable progress in our understanding of the sequence of molecular and structural events that mediate the response of endothelial cells to oxidants and nitrosants. In addition, substantial experimental evidence demonstrates improvement of endothelial barrier dysfunction with antioxidant strategies. However, no significant benefits have been observed, so far, in clinical trials of antioxidants for the treatment of endothelial barrier dysfunction. This article will review the available evidence implicating ROS and RNS in endothelial barrier dysfunction, explore potential underlying mechanisms, and identify areas of further research.

Transendothelial flow inhibits neutrophil transmigration through a nitric oxide-dependent mechanism: potential role for cleft shear stress

Endothelial cells in vivo are well known to respond to parallel shear stress induced by luminal blood flow. In addition, fluid filtration across endothelium (transendothelial flow) may trigger nitric oxide (NO) production, presumably via shear stress within intercellular clefts. Since NO regulates neutrophil-endothelial interactions, we determined whether transendothelial flow regulates neutrophil transmigration. Interleukin-1β-treated human umbilical vein endothelial cell (HUVEC) monolayers cultured on a polycarbonate filter were placed in a custom chamber with or without a modest hydrostatic pressure gradient (ΔP, 10 cmH2O) to induce transendothelial flow. In other experiments, cells were studied in a parallel plate flow chamber at various transendothelial flows (ΔP = 0, 5, and 10 cmH2O) and luminal flows (shear stress of 0, 1, and 2 dyn/cm2). In the absence of luminal flow, transendothelial flow reduced transmigration of freshly isolated human neutrophils from 57% to 14% ( P < 0.05) and induced an increase in NO detected with a fluorescent assay (DAF-2DA). The NO synthase inhibitor l-NAME prevented the effects of transendothelial flow on neutrophil transmigration, while a NO donor (DETA/NO, 1 mM) inhibited neutrophil transmigration. Finally, in the presence of luminal flow (1 and 2 dyn/cm2), transendothelial flow also inhibited transmigration. On the basis of HUVEC morphometry and measured transendothelial volume flow, we estimated cleft shear stress to range from 49 to 198 dyn/cm2. These shear stress estimates, while substantial, are of similar magnitude to those reported by others with similar analyses. These data are consistent with the hypothesis that endothelial cleft shear stress inhibits neutrophil transmigration via a NO-dependent mechanism.

Heparin-Binding EGF-like Growth Factor Decreases Neutrophil–Endothelial Cell Interactions

BACKGROUND

Hyperadhesiveness of neutrophils (PMN) to vascular endothelial cells (EC) followed by neutrophil transendothelial migration play important roles in the initiation of ischemia/reperfusion (I/R)-mediated injury. We investigated whether the ability of heparin-binding EGF-like growth factor (HB-EGF) to decrease intestinal injury after intestinal I/R is mediated, in part, by its ability to affect PMN-EC interactions and EC junctional integrity.

MATERIALS AND METHODS

Human umbilical vein EC monolayers were treated with HB-EGF (100 ng/mL) or phosphate-buffered saline followed by anoxia/reoxygenation (A/R). Simultaneously, labeled human PMN were treated with HB-EGF or phosphate-buffered saline and then co-incubated with EC for determination of PMN-EC adherence and PMN transendothelial migration. EC junctional integrity was also determined.

RESULTS

PMN-EC adhesion increased after exposure of EC to A/R compared to EC exposed to normoxia (87% versus 64% binding, P < 0.05, Wilcoxon rank sum test). A/R-induced PMN-EC hyperadherence was significantly decreased by treatment of PMN with HB-EGF compared to nontreated cells (51% versus 87% binding, P < 0.05). HB-EGF significantly decreased PMN transendothelial migration and also augmented EC tight junctional integrity after A/R.

CONCLUSIONS

HB-EGF significantly reduces A/R-induced PMN-EC adhesion and PMN transendothelial migration and augments junctional integrity in vitro. Thus, HB-EGF acts not only as a potent cytoprotective agent for the intestine, but as an anti-inflammatory agent as well.

Nitric oxide inhibits enterocyte migration through activation of RhoA-GTPase in a SHP-2-dependent manner

Diseases of intestinal inflammation like necrotizing enterocolitis (NEC) are associated with impaired epithelial barrier integrity and the sustained release of intestinal nitric oxide (NO). NO modifies the cytoskeletal regulator RhoA-GTPase, suggesting that NO could affect barrier healing by inhibiting intestinal restitution. We now hypothesize that NO inhibits enterocyte migration through RhoA-GTPase and sought to determine the pathways involved. The induction of NEC was associated with increased enterocyte NO release and impaired migration of bromodeoxyuridine-labeled enterocytes from terminal ileal crypts to villus tips. In IEC-6 enterocytes, NO significantly inhibited enterocyte migration and activated RhoA-GTPase while increasing the formation of stress fibers. In parallel, exposure of IEC-6 cells to NO increased the phosphorylation of focal adhesion kinase (pFAK) and caused a striking increase in cell-matrix adhesiveness, suggesting a mechanism by which NO could impair enterocyte migration. NEC was associated with increased expression of pFAK in the terminal ileal mucosa of wild-type mice and a corresponding increase in disease severity compared with inducible NO synthase knockout mice, confirming the dependence of NO for FAK phosphorylation in vivo and its role in the pathogenesis of NEC. Strikingly, inhibition of the protein tyrosine phosphatase SHP-2 in IEC-6 cells prevented the activation of RhoA by NO, restored focal adhesions, and reversed the inhibitory effects of NO on enterocyte migration. These data indicate that NO impairs mucosal healing by inhibiting enterocyte migration through activation of RhoA in a SHP-2-dependent manner and support a possible role for SHP-2 as a therapeutic target in diseases of intestinal inflammation like NEC.