Nitric oxide and postangioplasty restenosis: pathological correlates and therapeutic potential

Cu∥-loaded polydopamine coatings with in situ nitric oxide generation function for improved hemocompatibility

NO is the earliest discovered gas signal molecule which is produced by normal healthy endothelial cells, and it has many functions, such as maintaining cardiovascular homeostasis, regulating vasodilation, inhibiting intimal hyperplasia and preventing atherosclerosis in the blood system. Insufficient NO release is often observed in the pathological environment, for instance atherosclerosis. It was discovered that NO could be released from the human endogenous NO donor by many compounds, and these methods can be used for the treatment of certain diseases in the blood system. In this work, a series of copper-loaded polydopamine (PDA) coatings were produced through self-polymerization time for 24, 48 and 72 h. The chemical composition and structure, coating thickness and hydrophilicity of the different copper-loaded PDA coatings surfaces were characterized by phenol hydroxyl quantitative, X-ray photoelectron spectroscopy, ellipsometry atomic force microscopy and water contact angles. The results indicate that the thickness and the surface phenolic hydroxyl density of the PDA coatings increased with the polymerization time.This copper-loaded coating has glutathione peroxidase-like activity, and it has the capability of catalyzing NO releasing from GSNO. The surface of the coating showed desirable hemocompatibility, the adhesion and activation of platelets were inhibited on the copper-loaded coatings. At the same time, the formation of the thrombosis was also suppressed. These copper-loaded PDA coatings could provide a promising platform for the development of blood contact materials.

Diazeniumdiolation of protamine sulfate reverses mitogenic effects on smooth muscle cells and fibroblasts

After vascular interventions, endothelial cells are typically injured or lacking, resulting in decreased NO synthesis to maintain vascular health. Moreover, inflammation as a result of the tissue injury and/or the presence of an implanted foreign polymer such as a vascular graft causes excessive generation of reactive oxygen species (ROS) (e.g., superoxide), which can react with NO. The combination of the above creates a general decline in NO bioavailability, as well as oxidative stress due to less available NO to scavenge ROS. Localized NO delivery is an attractive solution to alleviate these issues; however, NO donors typically exhibit unpredictable NO payload release when using nitrosothiols or the risk of nitrosamine formation for synthetic diazeniumdiolates. The objective of this study was therefore to synthesize an NO donor from a biological peptide that could revert to its native form upon NO release. To this effect, protamine sulfate (PS), an FDA-approved peptide with reported vasodilator and anticoagulant properties, was diazeniumdiolated to form PS/NO. PS/NO showed diazeniumdiolate-characteristic UV peaks and NO release in physiological solutions and was capable of scavenging radicals to decrease oxidative stress. Furthermore, PS/NO selectively inhibits the proliferation of smooth muscle cells and adventitial fibroblasts, thereby reversing reported mitogenic properties of PS. Endothelial cell growth, on the other hand, was promoted by PS/NO. Finally, PS retained its anticoagulant properties upon diazeniumdiolation at clinically relevant concentrations. In conclusion, we have synthesized an NO prodrug from a biological peptide, PS/NO, that selectively inhibits proliferation of smooth muscle cells and fibroblasts, retains anticoagulant properties, and reverts back to its native PS form upon NO payload release.

Gelatin-siloxane nanoparticles to deliver nitric oxide for vascular cell regulation: synthesis, cytocompatibility, and cellular responses

Nitric oxide (NO) is an important mediator in cardiovascular system to regulate vascular tone and maintain tissue homeostasis. Its role in vascular cell regulation makes it promising to address the post-surgery restenosis problem. However, the application of NO is constrained by its high reactivity. Here, we developed a novel NO-releasing gelatin-siloxane nanoparticle (GS-NO NP) to deliver NO effectively for vascular cell regulation. Results showed that gelatin-siloxane nanoparticles (GS NPs) could be synthesized via sol-gel chemistry with a diameter of ∼200 nm. It could be modified into GS-NO NPs via S-nitrosothiol (RSNO) modification. The synthesized GS-NO NPs could release a total of ∼0.12 µmol/mg NO sustainably for 7 days following a first-order exponential profile. They showed not only excellent cytocompatibility, but also rapid intracellularization within 2 h. GS-NO NPs showed inhibition of human aortic smooth muscle cell (AoSMC) proliferation and promotion of human umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner, which is an important approach to prevent restenosis. With GS-NO NP dose at 100 µg/mL, the proliferation of AoSMCs could be slowed down whereas the growth of HUVECs was significantly promoted. We concluded that GS-NO NPs could have potential to be used as a promising nano-system to deliver NO for vascular cell regulation.

The formation of an anti-restenotic/anti-thrombotic surface by immobilization of nitric oxide synthase on a metallic carrier

Coronary stenosis due to atherosclerosis, the primary cause of coronary artery disease, is generally treated by balloon dilatation and stent implantation, which can result in damage to the endothelial lining of blood vessels. This leads to the restenosis of the lumen as a consequence of migration and proliferation of smooth muscle cells (SMCs). Nitric oxide (NO), which is produced and secreted by vascular endothelial cells (ECs), is a central anti-inflammatory and anti-atherogenic player in the vasculature. The goal of the present study was to develop an enzymatically active surface capable of converting the prodrug l-arginine, to the active drug, NO, thus providing a targeted drug delivery interface. NO synthase (NOS) was chemically immobilized on the surface of a stainless steel carrier with preservation of its activity. The ability of this functionalized NO-producing surface to prevent or delay processes involved in restenosis and thrombus formation was tested. This surface was found to significantly promote EC adhesion and proliferation while inhibiting that of SMCs. Furthermore, platelet adherence to this surface was markedly inhibited. Beyond the application considered here, this approach can be implemented for the local conversion of any systemically administered prodrug to the active drug, using catalysts attached to the surface of the implant.

Changes in ADMA and TAFI levels after stenting in coronary artery disease patients

The aim of this study was to examine the contribution of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS) and a novel marker of vascular endothelial dysfunction, and thrombin-activatable fibrinolysis inhibitor (TAFI), a risk factor for venous thrombosis, to the predisposition of coronary restenosis following stent implantation in coronary artery disease (CAD) patients. Thirty-seven patients with CAD were recruited from the Kobry El Obba Military Hospital, Cairo, Egypt. The patients were hospitalized for coronary angiography and coronary stenting (CS). Overnight fasting blood samples were collected from patients prior to CS and four months later for the determination of plasma ADMA and TAFI levels. The patients underwent follow-up coronary angiography to reveal in-stent restenosis. The results showed that plasma ADMA levels in CAD patients were significantly higher than those reported for healthy subjects. ADMA levels were significantly increased by 30% in CAD patients four months following CS. CAD patients who developed in-stent restenosis had a 35% increase in ADMA levels following CS. TAFI levels were not significantly changed after CS in CAD patients or in any of the subgroups. In conclusion, ADMA, but not TAFI, is linked to the predisposition of in-stent restenosis following CS.

Carotid restenosis is associated with plasma ADMA concentrations in carotid endarterectomy patients

BACKGROUND

The aim of this work has been to study the association between plasma asymmetric dimethylarginine (ADMA) concentrations and carotid stenosis in a group of 64 patients undergoing carotid endarterectomy (CEA).

METHODS

Arginine, ADMA and symmetric dimethylarginine (SDMA) were measured using capillary electrophoresis with UV detection. An evaluation of plasma concentrations of total cysteine (tCys) and total homocysteine (tHcy) was also performed.

RESULTS

Pearson's analysis show a positive correlation between ADMA and carotid stenosis (r=0.37, p=0.003), which is also confirmed after stepwise multiple linear regression analysis. ADMA plasma concentrations were significantly associated with tHcy (r=0.40, p=0.001) and to a lesser extent, even if not significantly, with tCys (r=0.23, p=0.07).

CONCLUSIONS

Our data suggest that plasma ADMA is involved in carotid narrowing after CEA intervention. This suggests that this molecule may have an important role in the events that lead to stenosis.

A novel predictor of restenosis and adverse cardiac events: asymmetric dimethylarginine

The aim of this study is to investigate if serum asymmetric dimethylarginine (ADMA) levels can predict restenosis and major adverse cardiac events (MACE) in patients who undergo percutaneous coronary interventions. The most important cause of restenosis following percutaneous coronary intervention is neointimal hyperplasia. Nitric oxide (NO) prevents the neointimal hyperplasia growing. Asymmetric dimethylarginine is a competitive inhibitor of NO synthesis. The effect of ADMA on the restenosis has not yet been investigated. A total of 105 (80 male and 25 female) patients were included in our study. All patients underwent elective percutaneous transluminal coronary angioplasty (PTCA) with bare metal stent implantation or direct stenting for one coronary artery between September 2004 and January 2006. All patients were clinically followed for a period of 6 months, and a control angiography was performed at the end of this period. The probrain natriuretic peptide (pro-BNP), high-sensitivity Creactive protein (hs-CRP), and ADMA levels of the patients were evaluated before the procedure and 6 months afterwards. Biochemical parameters and angiographic features were evaluated in order to determine if they could predict the development of restenosis and MACE by using univariate and multivariate Cox regression analysis. The 65 (61.9%) patients (50 males and 15 females) who had not developed restenosis were designated as Group 1. The 27 (25.7%) patients (21 males and 6 females) who had developed restenosis were designated as Group 2. In terms of predicting the development of restenosis, the presence of diabetes mellitus (hazard ratio [HR]: 2.78; confidence interval [CI]: 1.25-6.20; P = 0.01), type of lesion (HR: 1.89; CI: 1.01-3.55; P = 0.04), form of procedure (HR: 0.30; CI: 0.11-0.81; P = 0.01), and ADMA (HR: 4.08; CI: 1.73-9.62; P = 0.001) were found to be significant in univariate Cox regression analysis. In contrast, only the levels of ADMA were found to be a significant predictor of restenosis in the multivariate Cox regression analysis (HR: 3.02; CI: 1.16-7.84; P = 0.02). The restenosis prediction of ADMA levels continued after excluding the patients with diabetes mellitus in the univariate and multivariate Cox regression analysis (HR: 5.23; CI: 1.99-13.76; P = 0.001 and HR: 5.61; CI: 1.79-17.62; P = 0.003, respectively). Regarding the development of cardiac events, hs-CRP (HR: 1.03; CI: 1.00-1.06; P = 0.01) and ADMA (HR: 17.1; CI: 3.06-95.8; P = 0.001) were found to be significantly correlated with adverse cardiac events in univariate Cox regression analysis, whereas only ADMA levels were significant in the multivariate Cox regression analysis (HR: 2.83; CI: 1.27-6.31; P = 0.01). The levels of ADMA obtained before the procedure predict the development of restenosis and MACE in patients who underwent elective PTCA and bare metal stent procedures.

Oral administration of glycine in the prevention of restenosis after coronary angioplasty. A double blind placebo controlled randomized feasibility trial evaluating safety and efficacy of glycine in the prevention of restenosis after angioplasty

OBJECTIVES

Evaluation of safety, feasibility, and efficacy of oral administered glycine in prevention of angiographic restenosis six months after percutaneous coronary intervention (PCI).

BACKGROUND

The amino acid glycine modulates immunological response and enhances the production of endothelial derived nitric oxide (EDNO) factor. This factor has been shown to possess anti-atherosclerotic properties, actions of which are thought to reduce neo-intimal hyperplasia. Furthermore, glycine significantly elevates arginine serum levels. This amino acid has been extensively studied for its effects on the endothelium, nitric oxide (NO) metabolism and effects on several biochemical pathways interfering with the process of restenosis after PCI.

METHODS

A prospective double blind placebo controlled randomized study evaluated safety and feasibility of chronic oral administration of glycine. In addition, the efficacy was determined by evaluation of six months angiographic restenosis rates.

RESULTS

214 patients scheduled for elective PCI were randomized to receive glycine or placebo. At follow-up, there was no significant difference in side effects and in major adverse cardiac events (MACE) between both groups. Six-month angiograms revealed similar restenosis rates for the glycine group (17.5%) and for the placebo group (20.2%) (P = 0.82).

CONCLUSION

Chronic oral administration of glycine was safe and feasible and had similar side effects compared to placebo. However, chronic oral administration of glycine did not lead to a significant reduction in restenosis rates at six months after elective PCI.

Plasma ADMA predicts restenosis of arteriovenous fistula

Plasma levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide production, correlate with endothelial dysfunction and the development of cardiovascular events in patients with uremia. It is not known whether endothelial dysfunction contributes to the dysfunction of arteriovenous fistulas (AVFs) in hemodialysis patients. Here, we studied the predictive value of baseline plasma ADMA for symptomatic restenosis of an AVF after percutaneous transluminal angioplasty in dialysis patients. We obtained baseline plasma ADMA levels before percutaneous transluminal angioplasty in 100 consecutive patients with dysfunctional AVFs. Patients were followed up clinically for up to 6 mo after angioplasty for recurrent dysfunction. During the 6 mo after angioplasty, 46 patients experienced recurrent dysfunction of their AVF; of these, follow-up fistulography showed restenosis at the same location in 41, new stenosis at different locations in two, and no significant stenosis in three patients. Up to 60% of the patients with high levels of ADMA (>0.910 microM) had target lesion restenosis compared with 25% of those with low levels (<0.910 microM; P < 0.001). In multivariate analysis, plasma ADMA independently nearly tripled the risk for recurrent symptomatic stenosis of an AVF after percutaneous transluminal angioplasty (hazard ratio 2.65; 95% confidence interval 1.33 to 5.28). These results suggest a role for ADMA in the progression of symptomatic restenoses of AVFs after percutaneous transluminal angioplasty and call for preventive strategies that target ADMA and/or endothelial dysfunction to decrease the risk for AVF restenosis.

Regulation of eNOS-derived superoxide by endogenous methylarginines

The endogenous methylarginines, asymmetric dimethylarginine (ADMA) and N (G)-monomethyl- l-arginine (L-NMMA) regulate nitric oxide (NO) production from endothelial NO synthase (eNOS). Under conditions of tetrahydrobiopterin (BH 4) depletion eNOS also generates (*)O 2 (-); however, the effects of methylarginines on eNOS-derived (*)O 2 (-) generation are poorly understood. Therefore, using electron paramagnetic resonance spin trapping techniques we measured the dose-dependent effects of ADMA and L-NMMA on (*)O 2 (-) production from eNOS under conditions of BH 4 depletion. In the absence of BH 4, ADMA dose-dependently increased NOS-derived (*)O 2 (-) generation, with a maximal increase of 151% at 100 microM ADMA. L-NMMA also dose-dependently increased NOS-derived (*)O 2 (-), but to a lesser extent, demonstrating a 102% increase at 100 microM L-NMMA. Moreover, the native substrate l-arginine also increased eNOS-derived (*)O 2 (-), exhibiting a similar degree of enhancement as that observed with ADMA. Measurements of NADPH consumption from eNOS demonstrated that binding of either l-arginine or methylarginines increased the rate of NADPH oxidation. Spectrophotometric studies suggest, just as for l-arginine and L-NMMA, the binding of ADMA shifts the eNOS heme to the high-spin state, indicative of a more positive heme redox potential, enabling enhanced electron transfer from the reductase to the oxygenase site. These results demonstrate that the methylarginines can profoundly shift the balance of NO and (*)O 2 (-) generation from eNOS. These observations have important implications with regard to the therapeutic use of l-arginine and the methylarginine-NOS inhibitors in the treatment of disease.

Intra-arterial infusion of nitric oxide (NO) - first animal trial

OBJECTIVE

Nitric oxide (NO) is an important signaling molecule that acts in many tissues to regulate a diverse range of physiological processes. NO has been implicated in a number of cardiovascular diseases. Reduced basal NO synthesis or function may lead to: vasoconstriction, elevated blood pressure and thrombus formation. By contrast, overproduction of NO results in vasodilatation, hypotension, vascular leakage, and disruption of cell metabolism. The purpose of this study was to determine the effects of NO gas directly infused into the arteries.

METHODS

The study was performed on 28 rabbits and 10 pigs. We developed a device that enables quantitatively controlled infusion of NO gas, directly into the arteries.

RESULTS

We found that administration of NO gas via arteries caused widening of the blood vessels as well as increasing blood flow in the extremity. It emerges that. These effects persist up to 2-3 h after the NO infusion ceased. Although the NO breaks down when diffused in blood, its influence commences rapidly and continues for a relatively long time.

CONCLUSIONS

Our findings indicate that, administration of NO into blood vessels causes a long lasting vasodilatation and enhanced blood flow. Despite the fact that NO is broken down rapidly.

Apoptosis bcl-2 and nitrotyrosine expression in an angioplasty-restenosis rabbit: an experimental model

Apoptosis has been suggested to have an important role in the pathogenesis of restenosis in addition to cell migration and proliferation. The aim of the present study was to investigate in an experimental in vivo model the occurrence of apoptosis postangioplasty and its relation to bcl-2 and peroxynitrite detection. Eighteen hypercholesterolemic rabbits underwent transluminal angioplasty of the right iliac artery. The rabbits were sacrificed on the 1st, 2nd, 3rd, 7th, 15th, and 28th day postangioplasty (3 animals per time point) and both the angioplasted and non-injured arteries were studied. Apoptosis was assessed by the terminal uridine nick-end labeling method (TUNEL). Bcl-2 and peroxynitrite were detected by immunochemistry using anti-bcl-2 and anti-nitrotyrosine antibodies. In the angioplasted arteries the number of apoptotic cells was <or=1% of the total cell population in both media and neointima at any of the postangioplasty time points examined. Bcl-2 and nitrotyrosines were detected at all time points in the angioplasted arteries (vs. non-injured, P<0.001), showed similar localization and had the same peaks of expression both in the media (7th day: Bcl-2 66% and nitrotyrosines 74%) and neointima (15th day: Bcl-2 67% and nitrotyrosines 61%). In this experimental model we observed low apoptotic rates while bcl-2 and peroxynitrite products were detected. We can hypothesize that the detection of nitrotyrosines is related with reduced levels of nitric oxide resulting in increased expression of the bcl-2, preventing thus cell death due to either apoptosis or necrosis. Further studies are needed in order to elucidate their role in the restenosis process.

Reevaluating the role of phosphodiesterase inhibitors in the treatment of cardiovascular disease

First developed for clinical use in the late 1980s, the phosphodiesterase inhibitors were found to increase the levels of the ubiquitous second messenger cyclic adenosine monophosphate and could effect changes in vascular tone, cardiac function, and other cellular events. After several early studies using high doses of phosphodiesterase inhibitors in patients with severe heart failure suggested adverse consequences, they fell out of favor. However, recent investigations of phosphodiesterase inhibitors in patients with intermittent claudication have demonstrated profound benefits. Furthermore, these agents have proven useful in prevention of cerebral infarction and coronary restenosis, and their use in the treatment of heart failure is being reevaluated. The reemergence of phosphodiesterase inhibitors can be attributed to a better understanding of dosing and drug-specific pharmacology, the use of concomitant medications, and a recognition of unique ancillary properties; however, their use still requires caution.

Evidence for the pathophysiological role of endogenous methylarginines in regulation of endothelial NO production and vascular function

In endothelium, NO is derived from endothelial NO synthase (eNOS)-mediated L-arginine oxidation. Endogenous guanidinomethylated arginines (MAs), including asymmetric dimethylarginine (ADMA) and NG-methyl-L-arginine (L-NMMA), are released in cells upon protein degradation and are competitive inhibitors of eNOS. However, it is unknown whether intracellular MA concentrations reach levels sufficient to regulate endothelial NO production. Therefore, the dose-dependent effects of ADMA and L-NMMA on eNOS function were determined. Kinetic studies demonstrated that the Km for L-arginine is 3.14 microM with a Vmax of 0.14 micromol mg-1 min-1, whereas Ki values of 0.9 microM and 1.1 microM were determined for ADMA and L-NMMA, respectively. EPR studies of NO production from purified eNOS demonstrated that, with a physiological 100 microM level of L-arginine, MA levels of >10 microM were required for significant eNOS inhibition. Dose-dependent inhibition of NO formation in endothelial cells was observed with extracellular MA concentrations as low 5 microm. Similar effects were observed in isolated vessels where 5 microm ADMA inhibited vascular relaxation to acetylcholine. MA uptake studies demonstrated that ADMA and L-NMMA accumulate in endothelial cells with intracellular levels greatly exceeding extracellular concentrations. L-arginine/MA ratios were correlated with cellular NO production. Although normal physiological levels of MAs do not significantly inhibit NOS, a 3- to 9-fold increase, as reported under disease conditions, would exert prominent inhibition. Using a balloon model of vascular injury, approximately 4-fold increases in cellular MAs were observed, and these caused prominent impairment of vascular relaxation. Thus, MAs are critical mediators of vascular dysfunction following vascular injury.

Effects of local gene transfer of VEGF on neointima formation after balloon injury in hypercholesterolemic rabbits

Enhancement of the generation of nitric oxide (NO) and vascular endothelial growth factor (VEGF) are suggested to prevent restenosis after angioplasty. Accordingly, we tested whether the local delivery of L-arginine (L-Arg), a substrate for NO generation and the VEGF gene, alone or in combination, can influence neointima formation in hypercholesterolemic rabbits. Balloon injury of the iliac arteries was performed in 24 New Zealand White rabbits fed a 1% cholesterol diet for 3 weeks followed by a local infusion of: (1) pSG5VEGF165 plasmid alone (1000 microg); (2) pSG5VEGF165 (1000 microg) with L-Arg (800mg); (3) L-Arg (800mg) alone; and (4) L-Arg (800 mg) with naked pSVbeta-gal plasmid (1000 microg). The animals were kept on the hypercholesterolemic diets for a further 28 days, when vessels were taken for morphometric analysis and immunocytochemistry. Endogenous rabbit VEGF concentration in the plasma increased significantly at 7 days after injury (17.06 +/- 1.57 vs 23.01 +/- 1.9 pg/ml; p < 0.02) and remained elevated for up to 28 days (28.46 +/- 5.24; p < 0.01). Injured arteries exhibited strong immunocytochemical staining for rabbit VEGF. Rabbits that received a VEGF gene transfer revealed more prominent neointima formation, whereas treatment with L-Arg was associated with significantly less intimal thickness (p < 0.05). Local transfer of the VEGF gene does not inhibit neointima formation in hypercholesterolemic rabbits. Our results suggest that VEGF gene therapy applied locally in atherosclerotic arteries may not be beneficial.

Adenoviral gene vector tethering to nanoparticle surfaces results in receptor-independent cell entry and increased transgene expression

The present studies investigated the hypothesis that affinity immobilization of replication-defective adenoviruses (Ad) on the surfaces of biodegradable nanoparticles (NP) can improve transduction through uncoupling cellular uptake from the coxsackie-adenovirus receptor (CAR). Ad was tethered to the surfaces of polylactide-based NP that were surface-activated using a photoreactive polyallylamine-benzophenone-pyridyldithiocarboxylate polymer, which enabled (via thiol chemistry) the covalent attachment of Ad-binding proteins, either the recombinant D1 domain of CAR or an adenoviral knob-specific monoclonal antibody. Gene transfer by NP-Ad complexes was studied in relation to cellular uptake as a function of cell type and the character of NP-Ad binding. NP-Ad complexes, but not Ad applied with or without control nonimmune IgG-modified NP, significantly increased green fluorescent protein reporter expression in endothelioma and endothelial and arterial smooth muscle cells (SMC) in direct correlation to the extent of NP-Ad internalization. CAR-independent uptake of NP-Ad was confirmed by demonstrating inhibition of free Ad- but not NP-Ad complex-mediated transduction by knob protein. Complexes formulated with an Ad encoding inducible nitric oxide synthase inhibited growth of cultured SMC to a significantly greater extent than those with (GFP)Ad or (NULL)Ad or free vector. It is concluded that Ad-specific affinity tethering to biodegradable NP can significantly increase the level of gene expression via a CAR-independent uptake mechanism.

Coronary Stenting and Inflammation: Implications for Further Surgical and Medical Treatment

The introduction of percutaneous coronary interventions (PCI) with stent implant has substantially shifted the treatment of coronary artery disease. The current approach to coronary artery disease treatment includes first-choice PCI in selected subgroups; and once this therapy fails, frequently the patient is referred for coronary artery bypass graft surgery. However, evidence of chronic inflammatory reaction and endothelial dysfunction after PCI has been emerging and that might be interfering with patient outcome when surgical or medical treatments are subsequently required. The clinical significance of these complications after PCI, herein examined, has been less studied and needs better assessment. Also, the premise that coronary artery bypass graft surgery can safely be performed in patients with coronary stenting failure may not hold true, as graft patency might be adversely affected. Furthermore, the superimposed inflammatory reaction may blunt the efficacy of medical treatment.

Photoinduced nitric oxide release from nitrobenzene derivatives

A new type of photoinduced nitric oxide (NO) donors was designed from nitrobenzene derivatives. Visible-light irradiation of 2,6-dimethylnitrobenzenes bearing extended pi-electron systems at the 4-position revealed efficient NO release using ESR analysis and the Griess assay. Computational study and ultraviolet spectrum analysis suggested that the NO-releasing activity was closely related to the conformation of the nitro group, the absorption intensity, and the length of the conjugated pi-electron system. Employing the photodependent cytotoxicity of compound 14 against HCT116 human colon cancer cells, it was demonstrated that 4-substituted-2,6-dimethylnitrobenzene analogues are useful NO donors for the time- and site-controlled NO treatment.

Localized delivery of nitric oxide from hydrogels inhibits neointima formation in a rat carotid balloon injury model

Using novel nitric oxide (NO)-generating polymeric hydrogels that can be rapidly photopolymerized in situ, we can deliver NO locally at the site of vascular injury. Depending on material design, these poly(ethylene glycol) (PEG)-based hydrogels can generate NO for up to 50 d. This study demonstrates the ability of nitric oxide-generating hydrogels (PEG-Cys-NO) to influence key components of the restenosis cascade both in vitro and in vivo. PEG-Cys-NO hydrogels inhibited smooth muscle cell proliferation, increased endothelial cell proliferation, and inhibited platelet adhesion in vitro. Moreover, in vivo, PEG-Cys-NO hydrogels inhibited intimal thickening in a rat carotid balloon injury model. The perivascular application of NO-generating polymers post-injury reduced neointima formation at 14 d by approximately 80% compared to controls (intimal area/medial area (I/M): PEG-Cys-NO=0.20+/-0.17, control=0.84+/-0.19, p<0.00002; intimal thickness: PEG-Cys-NO=12+/-10 microm, control=60+/-18 microm, p<0.00002). Treatment with the PEG-Cys-NO hydrogels caused a significant decrease in the per cent of proliferating cell nuclear antigen positive medial cells (29+/-5%) at 4 d as compared to treatment with the control hydrogels (51+/-1%, p<0.02). Additionally, vessel re-endothelialization at 14 d was slightly enhanced in the presence of the NO-generating hydrogels. These data indicate that localized delivery of NO from these hydrogels can significantly inhibit neointima formation in a rat carotid balloon injury model and suggest that these materials may be useful in preventing restenosis.

Selective nitros(yl)ation induced in vivo by a nitric oxide-donating cyclooxygenase-2 inhibitor: a NObonomic analysis

Nitric oxide (NO) enhances anti-inflammatory drug action. Through a metabonomics approach termed "NObonomics," the effects of a prototypic NO donor (organic nitrate)-cyclooxygenase-2 inhibitor hybrid (NO-coxib), NMI-1093, on the NO metabolite status of the circulation and major organs have been profiled in vivo in the rat. An oral anti-inflammatory NMI-1093 bolus elicited acute tissue-, time-, and dose-dependent changes in oxidative and nitroso/nitrosyl NO metabolites. Gastric N-nitrosation and hepatic S-nitrosation and heme nitrosylation emerged as sensitive indices of this NO-coxib's metabolism. Acute NMI-1093-induced nitros(yl)ation correlated positively as a function of nitrate plus nitrite formation across all organs examined, suggesting a unifying in vivo mechanism consequent to NMI-1093 biotransformation that links oxidative and nitros(yl)ative routes of NO chemical biology and thereby may support downstream NO signaling. NMI-1093 depressed erythrocyte nitros(yl)ation, likely by inhibiting cellular carbonic anhydrase and shifting the intracellular balance between nitrogen oxides and carbonates. Glutathione-S-transferase or cytochrome P450 inhibitors also attenuated NMI-1093's NO metabolism in a compartment-selective fashion. Although not itself a NO donor, the des-nitro coxib analog of NMI-1093 influenced basal NO metabolite profiles, implicating a cyclooxygenase-NO synthase interaction in physiological NO regulation. By detailing the global NO metrics of a unique coxib bearing a popular NO-donor pharmacophore (i.e., a nitrate moiety) and defining some critical mechanistic determinants, this study demonstrates how NObonomics can serve as valuable tool in helping elucidate NO systems biology and the effect of NO-donor and non-NO-donating therapeutics thereon.

Influence of different therapeutic strategies on exhaled NO and lung inflammation in asthma and COPD

Nitric oxide (NO), a simple free radical gas, elicits a diverse range of physiological and pathophysiological effects, and plays an important role in pulmonary diseases. Nitrosative stress and nitration of proteins in airway epithelium maybe responsible for steroid resistance in asthma and their ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD. Here, we have reviewed the potential role of NO modulators (NO synthase inhibitors and NO donors), which if given on a regular basis may have clinical benefit in asthma and COPD.

External beam radiation therapy reduces the rate of re-stenosis in patients treated with femoral stenting: results of a randomised study

BACKGROUND AND PURPOSE

To evaluate the feasibility and efficacy of external beam irradiation (EBI) for the prevention of re-stenosis due to neointimal hyperplasia, after percutaneous transluminal angioplasty (PTA) and stent placement of the superficial femoral artery.

PATIENTS AND METHODS

A total of 60 patients with the diagnosis of superficial femoral artery stenoses or occlusions due to peripheral arterial obstructive disease underwent PTA and implantation of a self-expandable stent at their superficial femoral artery. After the procedure, patients were randomised and 30 of them received EBI (6 MV photons, total dose 24 Gy in six fractions in 2 weeks), while the rest 30 received no radiation therapy.

RESULTS

EBI was technically feasible in all patients, without serious radiation related side effects. Overall, a statistically significant difference was observed in stenosis categories between the two groups at 6 months follow-up (P=0.04). More specifically, significantly more patients in the control group presented with stenosis greater or equal than 70% [EBI group 30% (9/30); control group 66.7% (20/30); P=0.009]. This difference in the percentage of re-stenosis had as a consequence significantly lower re-intervention rates among the patients of the irradiated group [17% (5/30) versus 47% (14/30); P=0.025] during the 6 months follow-up period. We also observed that the irradiated patients had re-stenosis at the stent ends, while the non-irradiated had re-stenosis at the stent ends and the lumen. Three of the irradiated patients, who discontinued the anti-platelet treatment, have shown thrombosis of the irradiated artery during the first month from the completion of the treatment.

CONCLUSIONS

It is our belief that EBI is a feasible, safe and effective method for the prevention of neointimal hyperplasia at the superficial femoral artery. Further studies are deemed necessary to optimise the radiotherapy schedule.

Combination of Paclitaxel and Nitric Oxide as a Novel Treatment for the Reduction of Restenosis

The combination of a nitric oxide (NO) donor and a paclitaxel-NO donor conjugate coated on a vascular stent was tested in a rabbit iliac artery model of stenosis as a potential therapy for restenosis. Paclitaxel was conjugated with a NO donor at the 7-position to give compound 7. An adamantane-based NO donor 14 was synthesized and combined with 7 to provide a burst of NO in the first few critical hours following injury to the vessel wall. Both 7 and 14 demonstrated antiproliferative activity (IC(50) = 20 nM and 15 microM, respectively) and antiplatelet activity (IC(50) = 10 and 1 microM, respectively). Stents were coated with a layer of a polymer containing test compounds. The total amount of NO eluted from the stents after a 6 h implantation in the rabbit iliac artery was 35%, 95%, and 69% of the original content for the stents coated with 7, 14, and the combination of 7 and 14, respectively. The antistenotic activity of 7 and 14 was determined in a 28-day rabbit model with two control groups (uncoated stents and polymer-coated stents) and two study groups (paclitaxel-coated stents and stents coated with the combination of 7 and 14). Polymer-coated stents caused inflammation and increased stenosis by 39% when compared to the uncoated stents. The stents coated with 7 plus 14 were as good as the uncoated stents, 41% better than the polymer-coated stents and 34% better than the paclitaxel-coated stents. These data indicate a beneficial effect of adding NO to an antiproliferative agent (paclitaxel) and suggest a potential therapeutic combination for the treatment of stenotic vessel disease.

Adenoviral transfer of endothelial nitric oxide synthase attenuates lesion formation in a novel murine model of postangioplasty restenosis

OBJECTIVE

Restenosis remains a major late complication of percutaneous transluminal coronary angioplasty (PTCA), for which the development of prevention strategies has thus far been hampered by the lack of a representative and practical animal model. We have, therefore, developed a murine model of PTCA-induced restenosis.

METHODS AND RESULTS

Rigid probe angioplasty of pre-existing atherosclerotic lesions in the carotid arteries of ApoE-deficient mice was found to result in an increase in lesion size (0.14+/-0.04x10(5) microm2 to 0.42+/-0.09x10(5) microm2, P=0.007) with a smooth muscle cell-rich, fibrotic lesion morphology. In an additional experiment, lesions were incubated immediately after angioplasty with adenovirus bearing an endothelial nitric oxide synthase (eNOS) transgene (Ad.APT.eNOS), or an "empty" control virus (Ad.APT.empty) at a titer of 1.5x10(9) pfu/mL. Ad.APT.eNOS treatment was seen to lead to a 73.1% reduction in plaque size (0.27+/-0.04x10(5) microm2 versus 1.02+/-0.39x10(5) microm2, P=0.07), which translated to a significantly lowered average degree of stenosis (33.6+/-4.1% versus 74.6+/-14.0%, P=0.02). Ad.APT.eNOS also decreased lesional collagen content from 29.1% to 4.8% (P<0.001).

CONCLUSIONS

We believe that we have established a representative murine model of postangioplasty restenosis, which may serve to elucidate the mechanisms underlying restenosis and to evaluate potential antirestenotic therapies.

S-nitrosothiols inhibit uterine smooth muscle cell proliferation independent of metabolism to NO and cGMP formation

S-nitrosothiols (RSNOs) are important mediators of nitric oxide (NO) biology. The two mechanisms that appear to dominate in their biological effects are metabolism leading to the formation of NO and S-nitrosation of protein thiols. In this study we demonstrate that RSNOs inhibit uterine smooth muscle cell proliferation independent of NO. The antiproliferative effects of NO on vascular smooth muscle are well defined, with the classic NO-dependent production of cGMP being demonstrated as the active pathway. However, less is known on the role of NO in mediating uterine smooth muscle cell function, a process that is important during menstruation and pregnancy. The RSNOs S-nitrosoglutathione and S-nitroso-N-acetyl pencillamine inhibited growth factor-dependent proliferation of human and rat uterine smooth muscle cells (ELT-3). Interestingly, these cells reduced RSNOs to generate NO. However, use of NO donors and other activators of the cGMP pathway failed to inhibit proliferation. These findings demonstrate the tissue-specific nature of responses to NO and demonstrate the presence of a RSNO-dependent but NO-independent pathway of inhibiting DNA synthesis in uterine smooth muscle cells.

Prospective evaluation of hydroperoxide plasma levels and stable nitric oxide end products in patients subjected to angioplasty for coronary artery disease

BACKGROUND

Oxidative stress appears to be involved in several processes that contribute to atherogenesis and restenosis following vascular intervention.

METHODS

The aim of our study was to evaluate prospectively the plasma concentrations of a hydroperoxide (ROOH) and nitric oxide end product (NO(x)) in patients subjected to coronary angioplasty (PTCA) and routine control angiography 6 months after the initial procedure. We prospectively studied 48 consecutive patients (39 men, nine women, mean age 52 years) with stable angina who underwent successful elective angioplasty. A vascular segment was considered successfully treated when the residual luminal narrowing in the dilated segment immediately after angioplasty was <50%. Angiographic follow-up was obtained in all of the patients. Plasma samples were drawn at baseline (before angioplasty) and serially after angioplasty (1, 3 and 6 months afterwards). Hydroperoxides were determined by the FOX II assay (ferrous oxidation in xylenol orange, Pierce Rockford, IL). Nitrate was converted in the presence of NO3 reductase. The Griess reagent was used for the measurement of NO2.

RESULTS

The overall angiographic restenosis rate was 35%. There were no significant differences in clinical variables between the patients with or without restenosis. The baseline levels (0.8+/-0.09 vs. 0.6+/-0.2 micromol/l) as well as the concentrations of authentic lipid hydroperoxide in plasma after 1 month (0.7+/-0.09 vs. 1.0+/-0.2 micromol/l) and 6 months (0.8+/-0.1 vs. 1.0+/-0.2 micromol/l) were similar in both groups. Three months after the angioplasty a significant increase in the ROOH level was noticed in the patients with restenosis (0.9+/-0.1 vs. 1.4+/-0.2, P=0.04). Plasma levels of NO(x) were similar in both groups at baseline (23.6+/-2.1 vs. 22.7+/-2.6 micromol/l) and 1 month after procedure (24.4+/-2.2 vs. 23.4+/-3.3 micromol/l). However, in patients with restenosis significant decreases in stable NO end products were observed 3 and 6 months after PTCA (18.1+/-1.5 vs. 13.3+/-1.7, P=0.04; 14.2+/-1.0 vs. 8.7+/-1.3, P=0.02, respectively).

CONCLUSIONS

In patients with angiographic restenosis a significant increase in lipid peroxidation accompanied by a reduction in the stable end products of nitric oxide in plasma is observed several months after PTCA.

Nitric oxide, nitrotyrosine, and nitric oxide modulators in asthma and chronic obstructive pulmonary disease

Nitric oxide (NO), a simple free-radical gas, elicits a diverse range of physiologic and pathophysiologic effects, and plays an important role in pulmonary diseases. Nitrosative stress and nitration of proteins in airway epithelium may be responsible for steroid resistance in asthma and their ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD. In this article, we review the potential role of NO modulators (NO synthase inhibitors and NO donors), which, if given on a regular basis, may have clinical benefit in asthma and COPD.

Novel substrates for nitric oxide synthases

Enzymatic generation of nitric oxide (NO) by nitric oxide synthase (NOS) consists of two oxidation steps. The first step converts L-arginine to N(G)-hydroxy-L-arginine (NOHA), a key intermediate, and the second step converts NOHA to NO and L-citrulline. To fully probe the substrate specificity of the second enzymatic step, an extensive structural screening was carried out using a series of N-alkyl (and N-aryl) substituted-N'-hydroxyguanidines (1-14). Among the eleven N-alkyl-N'-hydroxyguanidines evaluated, N-n-propyl (2), N-iso-propyl (3), N-n-butyl (4), N-s-butyl (5), N-iso-butyl (6), N-pentyl (8) and N-iso-pentyl (9) derivatives were efficiently oxidized by the three isoenzymes of NOS (nNOS, iNOS and eNOS) to generate NO. N-Butyl-N'-hydroxyguanidine (4) was the best substrate for iNOS (K(m)=33 microM) and N-iso-propyl-N'-hydroxyguanidine (3) was the best substrate for nNOS (K(m)=56 microM). When the alkyl substituents were too small (such as ethyl 1) or too large (such as hexyl 10 and cyclohexyl 11), the activity decreased significantly. This suggests that the van der Waals interaction between the alkyl group and the hydrophobic cavity in the NOS active site contributes significantly to the relative reactivity of compounds 3-11. Moreover, five N-aryl-N'-hydroxyguanidines were found to be good substrates for iNOS, but not substrates for eNOS and nNOS. N-phenyl-N'-hydroxyguanidine was the best substrate among them (K(m)=243 microM). This work demonstrates that N-alkyl substituted hydroxyguanidine compounds are novel NOS substrates which 'short-circuit' the first oxidation step of NOS, and N-aryl substituted hydroxyguanidine compounds are isoform selective NOS substrate.

Augmentation of intrapericardial nitric oxide level by a prolonged-release nitric oxide donor reduces luminal narrowing after porcine coronary angioplasty

BACKGROUND

Nitric oxide (NO) is a potent vasodilator and antiplatelet agent that suppresses vascular smooth muscle cell proliferation. Hypothesizing that generating NO in the pericardial space would reduce luminal narrowing after coronary angioplasty without affecting systemic hemodynamics, we have determined the effect of a novel NO donor on vascular healing after balloon overstretch.

METHODS AND RESULTS

Diazeniumdiolated bovine serum albumin (D-BSA; molecular weight 74 kDa, half-life for NO release 20 days) was radioiodinated and found by intravital gamma-imaging to have a longer residence time in pig pericardium than a low-molecular-weight (0.5 kDa) analogue (22 versus 4.6 hours, respectively). Intrapericardial injection of D-BSA immediately before 30% overstretch of normal left anterior descending and left circumflex coronary arteries dose dependently reduced the intimal/medial area ratio by up to 50% relative to controls treated with underivatized albumin when measured 2 weeks after intervention. Positive remodeling was also noted, which increased luminal area relative to control.

CONCLUSIONS

Perivascular exposure of coronary arteries to NO via intrapericardial D-BSA administration reduced flow-restricting lesion development after angioplasty in pigs without causing significant systemic effects. The data suggest that intrapericardial delivery of NO donors for which NO release rates and pericardial residence times are matched and optimized might be a beneficial adjunct to coronary angioplasty.

Pharmacological approaches to preserving and restoring coronary endothelial function

There is compelling evidence that the endothelium is critical to normal coronary vascular function and that endothelial dysfunction, generally indicated by an impairment of endothelium-dependent vasodilatation, is an important component of coronary artery disease (CAD). Endothelial cells synthesise and release a number of factors, including prostacyclin, nitric oxide (NO), endothelium-derived hyperpolarising factor (EDHF) and endothelin, which are important in the regulation of vascular tone and the control of platelet and leukocyte adhesion, aggregation and migration. NO appears to be the critical factor in the preservation of normal coronary vascular function and there is a well-established correlation between CAD and an impairment of NO activity. Thus, to preserve endothelial function, drugs have been used to either increase the synthesis of NO, or to decrease its breakdown. Fortuitously, compounds such as the HMG-CoA reductase inhibitors, angiotensin (AT) converting enzyme inhibitors (ACEIs), AT receptor antagonists and oestrogen, which have been introduced into clinical practice because of other beneficial effects, have also been shown to improve coronary endothelial function through a variety of mechanisms. In addition, L -arginine, the substrate for NO synthesis, and the anti-oxidants ascorbate and alpha-tocopherol, are able to increase NO synthesis and bioavailability respectively. Studies in experimental animals strongly support the ability of these agents to enhance the activity of endothelium-derived NO but clinical trials have failed to demonstrate reversal of established CAD. Whether these agents preserve endothelial function and prevent the development of CAD remains to be established.

Nutritional aspects of nitric oxide: human health implications and therapeutic opportunities

Nitric oxide (NO), the most potent natural vasorelaxant known, has close historical ties to cardiovascular physiology, despite NO's rich physiologic chemistry as an ubiquitous, signal-transducing radical. Aspects of NO biology critical to gastrointestinal health and, consequently, nutritional status are increasingly being recognized. Attempts are underway to exploit the gastrointestinal actions of NO for therapeutic gain. Cross-talk between NO and micronutrients within and outside the gastrointestinal system affects the establishment or progression of several diseases with pressing medical needs. These concepts imply that NO biology can influence nutrition and be nutritionally modulated to affect mammalian (patho)physiology. At least four nutritional facets of NO biology are at the forefront of contemporary biomedical research: 1) NO as modulator of feeding behavior and mediator of gastrointestinal homeostasis; 2) NO supplementation as a therapeutic modality for preserving gastrointestinal health; 3) interactions among elemental micronutrients (e.g., zinc), NO, and inflammation as potential contributors to diarrheal disease; and 4) vitamin micronutrients (e.g., vitamins E and C) as protectors of NO-dependent vascular function. Discussion of extant data on these topics prompts speculation that future research will broaden NO's nutritional role as an integrative signaling molecule supporting gastrointestinal and nutritional well-being.

Emerging therapeutic targets in nitric oxide-dependent cardiac disease

Nitric oxide (NO) is a free radical gas that plays paracrine/autocrine and intracrine roles in maintaining physiological cardiovascular performance. In the coronary circulation, NO mediates endothelium-dependent vasodilator responses to shear stress and agonist-induced responses to neurohumoral stimulation. In the heart, NO modulates myocardial relaxation, beta-adrenergic responses, mitochondrial respiration and substrate metabolism and excitation-contraction coupling. Endothelial dysfunction and the resulting decrease in the production, bioavailability and/or second messenger response-coupling has been implicated in coronary artery disease and complications associated with restenosis following coronary angioplasty, stent placement and coronary artery bypass grafting (CABG). However, there are a number of pathophysiological conditions (ischaemia-reperfusion, cardiac transplant rejection, myocarditis, sepsis) in which unregulated overproduction of NO and other reactive oxygen species (ROS) results in deleterious effects on cardiac function. Given the importance of NO in cardiac physiology/pathophysiology it may serve as a potential target for interventions aimed at deterring therapeutic failures of percutaneous or surgical treatments of cardiac disease as well as serving as a primary medical intervention. This review will examine the function of NO in mediating/modulating cardiac function, stressing the concept that, depending on the milieu, NO has the potential to exert either beneficial or deleterious effects on cardiac function. Moreover, this review will summarise studies in laboratory models and human studies in which NO activity, production, availability, or second messenger activation has been enhanced or inhibited in order to provide new insight for future targeting of this system for drug development.

ESDN, a novel neuropilin-like membrane protein cloned from vascular cells with the longest secretory signal sequence among eukaryotes, is up-regulated after vascular injury

A novel cDNA has been isolated from primary culture of human coronary arterial cells by a signal sequence trap method, and designated ESDN (endothelial and smooth muscle cell-derived neuropilin-like molecule). ESDN is a type-I transmembrane protein with the longest cleavable secretory signal sequence among eukaryotes. ESDN contains a CUB domain and a coagulation factor V/VIII homology domain, which reminds us of the structure of neuropilins. ESDN also harbors an LCCL domain, which is shared by Limulus factor C and Coch. Mouse and rat counterparts were also identified revealing >84% amino acid identity with human ESDN. The human ESDN gene was mapped between D3S1552 and D3S1271. Northern blot analysis showed that ESDN mRNA was expressed in various tissues; particularly highly expressed in cultured vascular smooth muscle cells. The ESDN expression was up-regulated in platelet-derived growth factor-BB-stimulated vascular smooth muscle cells in vitro and neointima of the balloon-injured carotid artery in vivo. Overexpression of ESDN in 293T cells suppressed their bromodeoxyuridine uptake. In addition, ESDN protein was strongly expressed in nerve bundles in rodents. Thus, ESDN is considered to play a role in regulation of vascular cell growth and may have a wide variety of functions in other tissues including the nervous system, like neuropilins.

Oxidants and antioxidants in atherosclerosis

The oxidative theory suggests that LDL oxidation contributes to atherogenesis, implying that attenuation of this process by antioxidants should decrease atherosclerosis. However, a causative link between LDL oxidation and atherogenesis is not firmly established. It requires the identification of the oxidants that are responsible for the initiation of LDL oxidation, and an understanding of the modified moieties that are responsible for the proatherogenic activities of oxidized LDL. The present review summarizes recent data on potential biological oxidants for LDL in the vessel wall, and discusses the antiatherogenic role(s) of selected antioxidants.