Nitric oxide inhibition enhances platelet aggregation in experimental anti-Thy-1 nephritis

New Disposable Nitric Oxide Sensor Fabrication Using GaN Nanowires

Gallium nitride (GaN) nanowires anchored on the surface of cost-effective pencil graphite electrodes (PGEs) have been developed as a new disposable nitric oxide (NO) sensor through a hydrothermal method followed by annealing treatment. The as-obtained nanomaterials were examined by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and EIS. Concurrently, the electrocatalytic performance has been analyzed using cyclic voltammetry and amperometric measurements. The experimental results exhibit good electrochemical sensing performance toward the generated NO in NO2 - with a wide linear detection range of 1.0 μM to 1.0 mM with a correlation coefficient of 0.999 and a detection limit of 0.180 μM. In addition, the GaN nanowire-modified PGE surface showed high selectivity for the detection of NO as compared to other relevant biomolecules. This confirms that the PGE/GaN nanowire is a new promising electrochemical sensor for the sensitive detection of NO.

Selective and Sensocompatible Electrochemical Nitric Oxide Sensor with a Bilaminar Design

Macrophages mediate mammalian inflammation in part by the release of the gasotransmitter, nitric oxide (NO). Electrochemical methods represent the best means of direct, continuous measurement of NO, but monitoring continuous release from immunostimulated macrophages remains analytically challenging. Long release durations necessitate consistent sensor performance (i.e., sensitivity and selectivity for NO) in proteinaceous media. Herein, we describe the fabrication of an electrochemical sensor modified by an electropolymerized 5-amino-1-naphthol (poly(5A1N)) film in conjunction with a fluorinated xerogel topcoat. The unique combination of these membranes ensures selective detection of NO that is maintained over extended periods of use (>24 h) in biological media without performance deterioration. The hydrophobic xerogel topcoat protects the underlying NO-selective poly(5A1N) film from hydration-induced desorption. The bilaminar sensor is then readily adapted for measurement of the temporal NO-release profiles from immunostimulated macrophages.

Nitric oxide permselectivity in electropolymerized films for sensing applications

The presence of biological interferents in physiological media necessitates chemical modification of the working electrode to facilitate accurate electrochemical measurement of nitric oxide (NO). In this study, we evaluated a series of self-terminating electropolymerized films prepared from one of three isomers of phenylenediamine (PD), phenol, eugenol, or 5-amino-1-naphthol (5A1N) to improve the NO selectivity of a platinum working electrode. The electrodeposition procedure for each monomer was individually optimized using cyclic voltammetry (CV) or constant potential amperometry (CPA). Cyclic voltammetry deposition parameters favoring slower film formation generally yielded films with improved selectivity for NO over nitrite and l-ascorbate. Nitric oxide sensors were fabricated and compared using the optimized deposition procedure for each monomer. Sensors prepared using poly-phenol and poly-5A1N film-modified platinum working electrodes demonstrated the most ideal analytical performance, with the former demonstrating the best selectivity. In simulated wound fluid, platinum electrodes modified with poly-5A1N films proved superior with respect to the NO sensitivity and detection limit.

A flow-cytometry assisted segregation of responding and non-responding population of endothelial cells for enhanced detection of intracellular nitric oxide production

Nitric oxide (NO) is an important paracrine substance released by the endothelium to regulate vasomotor tone. The constitutive levels of endothelium dependent NO production is low. However, it is induced significantly in response to certain environmental and biological stimuli. An accurate evaluation of such stimulus induced NO release is of pharmacological significance. We observed that the sensitivity of NO detection in endothelial cells is compromised by baseline fluorescence emanated from non-activated cells resulting in ambiguous detection. In order to measure NO levels in activated population independent of non-activated cells, we segregated DAF-FM loaded cells based on their fluorescence intensity using flow-cytometry. Specific agonists like bradykinin, VEGF and insulin enhanced the proportion of activated cells. This effect was partially blocked in presence of NO synthase inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME). We demonstrate that the fluorescence yield of activated population serves as a sensitive measure to evaluate agonist induced nitric oxide production in endothelial cells. Such increase in NO production in activated cells was also associated with increased eNOS phosphorylation at Ser-1177. While the endothelial cells showed heterogeneity with respect to NO production, immuno-phenotyping for endothelial cell-surface markers revealed a homogenous population.

Expression of eNOS in kidneys from hypertensive patients

Endothelium-derived nitric oxide (NO) is essential for maintenance and regulation of blood pressure. In animal models, altered endothelium-derived nitric oxide synthase (eNOS) expression and impaired NO generation are important factors for renal injury. However, the pattern of eNOS expression in the kidneys from hypertensive patients has not been well established. We have studied the eNOS immuno-expression in kidney biopsies from hypertensive patients. Compared to kidneys from normotensive individuals, there were no significant alterations of eNOS immuno-expression in the vasculature of patients with chronic essential hypertension. In contrast, the expression of eNOS was significantly decreased in the glomeruli and arterioles/small arteries of patients with malignant hypertension, particularly in those with significant intimal edema and myxoid degeneration or thrombi. Endothelial dysfunction is an important pathogenetic factor for chronic primary hypertension and eNOS plays a major role in the regulation of vascular tone and function. Unchanged eNOS in the kidney vasculature in chronic primary hypertension indicates that these patients have an ability to compensate. In patients with malignant hypertension, the expression of eNOS protein was diminished in the injured vasculature. Loss of the compensatory mechanism via continued release of NO to prevent vascular injury may be responsible for morphological changes typically seen in the renal vasculature in patients with accelerated hypertension.

Visfatin activates eNOS via Akt and MAP kinases and improves endothelial cell function and angiogenesis in vitro and in vivo: translational implications for atherosclerosis

Improving endothelial nitric oxide synthase (eNOS) bioactivity and endothelial function is important to limit native, vein graft, and transplant atherosclerosis. Visfatin, a NAD biosynthetic enzyme, regulates the activity of the cellular survival factor, Sirt1. We hypothesized that visfatin may improve eNOS expression, endothelial function, and postnatal angiogenesis. In human umbilical vein (HUVEC) and coronary artery endothelial cells, we evaluated the effects of recombinant human visfatin on eNOS protein and transcript expression and mRNA stability, in the presence and absence of visfatin RNA silencing. We also assessed visfatin-induced protein kinase B (Akt) activation and its association with src-tyrosine kinases, phosphorylation of Ser(1177) within eNOS in the presence and absence of phosphatidylinositol 3-kinase (PI 3-kinase) inhibition with LY-294002, and evaluated the contributory role of extracellular signal-regulated kinase 1/2. Finally, we determined the impact of visfatin on HUVEC migration, proliferation, inflammation-induced permeability, and in vivo angiogenesis. Visfatin (100 ng/ml) upregulated and stabilized eNOS mRNA and increased the production of nitric oxide and cGMP. Visfatin-treated HUVEC demonstrated greater proliferation, migration, and capillary-like tube formation but less tumor necrosis factor-alpha-induced permeability; these effects were decreased in visfatin gene-silenced cells. Visfatin increased total Akt and Ser(473)-phospho-Akt expression with concomitant rises in eNOS phosphorylation at Ser(1177); these effects were blocked by LY-2940002. Studies with PP2 showed that the nonreceptor tyrosine kinase, src, is an upstream stimulator of the PI 3-kinase-Akt pathway. Visfatin also activated mitogen-activated protein (MAP) kinase through PI 3-kinase, and mitogen/extracellular signal-regulated kinase inhibition attenuated visfatin-elicited Akt and eNOS phosphorylation. Visfatin-filled Matrigel implants showed an elevated number of infiltrating vessels, and visfatin treatment produced significant recovery of limb perfusion following hindlimb ischemia. These results indicate a novel effect of visfatin to stimulate eNOS expression and function in endothelial cells, via a common upstream, src-mediated signaling cascade, which leads to activation of Akt and MAP kinases. Visfatin represents a translational target to limit endothelial dysfunction, native, vein graft and transplant atherosclerosis, and improve postnatal angiogenesis.

Amelioration of anti-Thy1-glomerulonephritis by PPAR-γ agonism without increase of endothelial progenitor cell homing

Impaired glomerular endothelial integrity is pivotal in various renal diseases and depends on both the degree of glomerular endothelial injury and the effectiveness of glomerular endothelial repair. Glomerular endothelial repair is, in part, mediated by bone marrow-derived endothelial progenitor cells. Peroxisome proliferator activated receptor-γ (PPAR-γ) agonists have therapeutic actions independent of their insulin-sensitizing effects, including enhancement of endothelial progenitor cell function and differentiation. We evaluated the effect of PPAR-γ agonist rosiglitazone (4 mg·kg−1·day−1) on the course of anti-Thy1-glomerulonephritis in rats. Rosiglitazone limited the development of proteinuria and prevented plasma urea elevation (8.1 ± 0.4 vs. 12.5 ± 1.1 mmol/l, P = 0.002). Histologically, inflammatory cell influx was not affected, but rosiglitazone-treated rats did show fewer microaneurysmatic glomeruli on day 7 (26 ± 3 vs. 41 ± 5%, P = 0.01) and reduced activation of matrix production with reduced renal cortical transforming growth factor-β, plasminogen activator inhibitor type 1, and fibronectin-1 mRNA expression. However, bone marrow-derived endothelial cell glomerular incorporation was not enhanced (3.1 ± 0.4 vs. 3.6 ± 0.3 cells/glomerular cross section; P = 0.31). Rosiglitazone treatment in nonnephritic rats did not influence proteinuria, urea, or renal histology. In conclusion, treatment with PPAR-γ agonist rosiglitazone ameliorates the course of experimental glomerulonephritis in a nondiabetic model, but not through enhancing incorporation of bone marrow-derived endothelial cells in the glomerulus.

Uncoupling of the VEGF-endothelial nitric oxide axis in diabetic nephropathy: an explanation for the paradoxical effects of VEGF in renal disease

In many forms of experimental kidney diseases, renal VEGF is low, and administering VEGF can be shown to be protective. A paradox occurs in diabetes, in which renal VEGF levels are high and a deleterious effect of VEGF on kidney disease has been shown. We have hypothesized that endothelial dysfunction induced by hyperglycemia or other factors may underlie the pathogenic mechanisms of a high VEGF state. VEGF normally stimulates endothelial nitric oxide (NO) release and acts in concert with elevated NO levels as a trophic factor for vascular endothelium. The increased NO derived from the endothelial cell acts as an inhibitory factor that prevents excess endothelial cell proliferation, vascular smooth muscle cell proliferation, and macrophage infiltration. In the setting where NO bioavailability is reduced in diabetes, high levels of VEGF lead to excessive endothelial cell proliferation, stimulation of macrophage chemotaxis, and vascular smooth muscle cell activation. Consistent with this hypothesis is our recent observation that diabetes induced in endothelial NO-deficient mice results in clinical and histological features identical to human diabetic nephropathy. The discovery of the key role for impaired endothelial NO bioavailability in the stimulation of VEGF and VEGF-dependent disease may provide key insights into not only the pathogenesis of diabetic nephropathy but also the utility and hazard of administering VEGF as a treatment for kidney disease.

Nitric oxide and glomerulonephritis

Glomerulonephritis is a common clinical condition that is caused by immune-mediated injury to the kidney and is characterized by dysfunction of the glomerular capillary filtration barrier. Nitric oxide (NO), a ubiquitous molecule with many biological functions throughout the body, has been evaluated as an inflammatory mediator in these circumstances. NO may induce glomerular injury directly or may act via stimulation of a host of other inflammatory mediators. A variety of experimental models of glomerulonephritis have been studied including those induced by infusion of antibodies to the Thy1.1 antigen or glomerular basement membrane, Heymann nephritis, and autoimmune nephritis. In virtually all of these cases there is evidence of increased NO production. Excessive production of NO by inducible nitric oxide synthase (iNOS), derived from infiltrating immune cells or resident glomerular cells, nearly always is associated with increased glomerular injury. Interventions that inhibit this enzyme result in less proteinuria and diminished glomerular damage. In contrast, NO derived from endothelial nitric oxide synthase (eNOS) may limit glomerular disease by preserving endothelial cell integrity. There are only a limited number of studies that have evaluated the impact of NO in patients with glomerulonephritis. Although the bulk of evidence supports a role of NO as a pro-inflammatory mediator in glomerulonephritis, additional work is needed to show an association between altered NO production and the severity and outcome of disease in patients with this disease. It is hoped that better understanding of the role of NO in glomerulonephritis will lead to the development of therapies to ameliorate the disease.

Nitric oxide regulates the polyol pathway of glucose metabolism in vascular smooth muscle cells

Increased reduction of glucose via the polyol pathway enzyme aldose reductase (AR) has been linked to the development of secondary diabetic complications. Because AR is a redox-sensitive protein, which in vitro is readily modified by NO donors, we tested the hypothesis that NO may be a physiological regulator of AR. We found that administration of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) increased sorbitol accumulation in the aorta of nondiabetic and diabetic rats, whereas treatment with L-arginine (a precursor of NO) or nitroglycerine patches prevented sorbitol accumulation. When incubated ex vivo with high glucose, sorbitol accumulation was increased by L-NAME and prevented by L-arginine in strips of aorta from rats or wild-type, but not eNOS-deficient, mice. Exposure to NO donors also inhibited AR and prevented sorbitol accumulation in rat aortic vascular smooth muscle cells (VSMC) in culture. The NO donors also increased the incorporation of radioactivity in the AR protein immunoprecipitated from VSMC in which the glutathione pool was prelabeled with [35S]-cysteine. Based on these observations, we suggest that NO regulates the vascular synthesis of polyols by S-thiolating AR; therefore, increasing NO synthesis or bioavailability may be useful in preventing diabetes-induced changes in the polyol pathway.

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

A protective role for endothelial nitric oxide synthase in glomerulonephritis

In acute glomerulonephritis (GN), increased nitric oxide (NO) production occurs, suggesting a pathophysiological role for NO in the disease process. Although NO potentially could have both toxic as well as protective effects, its exact role in the pathophysiology of GN is unclear and may depend on the NOS isoform generating NO. The protective effects of NO such as prevention of leukocyte and platelet activation and adhesion have been attributed to NO generated by endothelial nitric oxide synthase (eNOS). Evidence for a beneficial role for eNOS includes the demonstration of reduced eNOS expression in experimental models of GN as well as human biopsy specimens that is mostly likely due to endothelial cell necrosis. Reduced NO production in GN also may occur through reaction of NO with superoxide anions or the myeloperoxidase (MPO)/hypochlorous acid (HOCL) system. Further evidence has been provided by the observation that in several experimental models of GN, glomerular injury is exacerbated following treatment with non-selective NO inhibitors. Finally, the development of GN is severely aggravated in mice lacking a functional gene for eNOS as compared to wild-type mice, providing direct support for a protective role of eNOS-derived NO in acute GN.