Inhibition of platelet activity by S-nitrosoglutathione during coronary angioplasty

Nitric oxide and thiols: Chemical biology, signalling paradigms and vascular therapeutic potential

Nitric oxide (• NO) interactions with biological thiols play crucial, but incompletely determined, roles in vascular signalling and other biological processes. Here, we highlight two recently proposed signalling paradigms: (1) the formation of a vasodilating labile nitrosyl ferrous haem (NO-ferrohaem) facilitated by thiols via thiyl radical generation and (2) polysulfides/persulfides and their interaction with • NO. We also describe the specific (bio)chemical routes in which • NO and thiols react to form S-nitrosothiols, a broad class of small molecules, and protein post-translational modifications that can influence protein function through catalytic site or allosteric structural changes. S-Nitrosothiol formation depends upon cellular conditions, but critically, an appropriate oxidant for either the thiol (yielding a thiyl radical) or • NO (yielding a nitrosonium [NO+ ]-donating species) is required. We examine the roles of these collective • NO/thiol species in vascular signalling and their cardiovascular therapeutic potential.

Effects of nitrite and far-red light on coagulation

Nitric oxide, NO, has been explored as a therapeutic agent to treat thrombosis. In particular, NO has potential in treating mechanical device-associated thrombosis due to its ability to reduce platelet activation and due to the central role of platelet activation and adhesion in device thrombosis. Nitrite is a unique NO donor that reduces platelet activation in that it's activity requires the presence of red blood cells whereas NO activity of other NO donors is blunted by red blood cells. Interestingly, we have previously shown that red blood cell mediated inhibition of platelet activation by adenosine diphosophate (ADP) is dramatically enhanced by illumination with far-red light that is likely due to photolysis of red cell surface bound NO congeners. We now report the effects of nitrite, far-red light, and their combination on several measure of blood coagulation using a variety of agonists. We employed turbidity assays in platelet rich plasma, platelet activation using flow cytometry analysis of a fluorescently labeled antibody to the activated platelet fibrinogen binding site, multiplate impedance-based platelet aggregometry, and assessment of platelet adhesion to collagen coated flow-through microslides. In all cases, the combination of far-red light and nitrite treatment decreased measures of coagulation, but in some cases mono-treatment with nitrite or light alone had no effect. Perhaps most relevant to device thrombosis, we observed that platelet adhesions was inhibited by the combination of nitrite and light treatment while nitrite alone and far-red light alone trended to decrease adhesion, but the results were mixed. These results support the potential of combined far-red light and nitrite treatment for preventing thrombosis in extra-corporeal or shallow-tissue depth devices where the far-red light can penetrate. Such a combined treatment could be advantageous due to the localized treatment afforded by far-red light illumination with minimal systemic effects. Given the role of thrombosis in COVID 19, application to treatment of patients infected with SARS Cov-2 might also be considered.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

A Versatile Surface Bioengineering Strategy Based on Mussel-Inspired and Bioclickable Peptide Mimic

In this work, we present a versatile surface engineering strategy by the combination of mussel adhesive peptide mimicking and bioorthogonal click chemistry. The main idea reflected in this work derived from a novel mussel-inspired peptide mimic with a bioclickable azide group (i.e., DOPA₄-azide). Similar to the adhesion mechanism of the mussel foot protein (i.e., covalent/noncovalent comediated surface adhesion), the bioinspired and bioclickable peptide mimic DOPA₄-azide enables stable binding on a broad range of materials, such as metallic, inorganic, and organic polymer substrates. In addition to the material universality, the azide residues of DOPA₄-azide are also capable of a specific conjugation of dibenzylcyclooctyne- (DBCO-) modified bioactive ligands through bioorthogonal click reaction in a second step. To demonstrate the applicability of this strategy for diversified biofunctionalization, we bioorthogonally conjugated several typical bioactive molecules with DBCO functionalization on different substrates to fabricate functional surfaces which fulfil essential requirements of biomedically used implants. For instance, antibiofouling, antibacterial, and antithrombogenic properties could be easily applied to the relevant biomaterial surfaces, by grafting antifouling polymer, antibacterial peptide, and NO-generating catalyst, respectively. Overall, the novel surface bioengineering strategy has shown broad applicability for both the types of substrate materials and the expected biofunctionalities. Conceivably, the "clean" molecular modification of bioorthogonal chemistry and the universality of mussel-inspired surface adhesion may synergically provide a versatile surface bioengineering strategy for a wide range of biomedical materials.

Integrated microfluidic device for the separation, decomposition and detection of low molecular weight S-nitrosothiols

S-nitrosothiols (RSNOs) are very important biomolecules that play crucial roles in many physiological and physiopathological processes. They act as NO-donors and are candidates for future medicines. Their identification and quantitation are therefore important for biomedical applications. One, two or more RSNOs can then be combined to design a drug and therefore, the quantification of each is important to establish an acceptable quality control process. Till date, miniaturized devices have been used to detect RSNOs based on their total quantitation without a preceding separation step. This study reports on an original and integrated microdevice allowing for the successive electrokinetic separation of low molecular weight RSNOs, their decomposition under metal catalysis, and their quantitation by amperometric detection of the produced nitrite in the end-channel arrangement, leading to their quantitation in a single run. For this purpose, a commercial SU-8/Pyrex microfluidic system was coupled to a portable and wireless potentiostat. Different operating and running parameters were optimized to achieve the best analytical data, allowing for an LOD equal to 20 μM. The simultaneous separation of S-nitrosoglutathione and S-nitrosocysteine was successfully obtained within 75 s. The proposed methodology using SU-8/Pyrex microfluidic devices opens new possibilities to investigate future drug candidates for NO-donors.

Pyrrole: An insight into recent pharmacological advances with structure activity relationship

Pyrrole is a heterocyclic ring template with multiple pharmacophores that provides a way for the generation of library of enormous lead molecules. Owing to its vast pharmacological profile, pyrrole and its analogues have drawn much attention of the researchers/chemists round the globe to be explored exhaustively for the benefit of mankind. This review focusses on recent advancements; pertaining to pyrrole scaffold, discussing various aspects of structure activity relationship and its bioactivities.

Regulation of protein function by S-nitrosation and S-glutathionylation: processes and targets in cardiovascular pathophysiology

Decades of chemical, biochemical and pathophysiological research have established the relevance of post-translational protein modifications induced by processes related to oxidative stress, with critical reflections on cellular signal transduction pathways. A great deal of the so-called ‘redox regulation’ of cell function is in fact mediated through reactions promoted by reactive oxygen and nitrogen species on more or less specific aminoacid residues in proteins, at various levels within the cell machinery. Modifications involving cysteine residues have received most attention, due to the critical roles they play in determining the structure/function correlates in proteins. The peculiar reactivity of these residues results in two major classes of modifications, with incorporation of NO moieties (S-nitrosation, leading to formation of proteinS-nitrosothiols) or binding of low molecular weight thiols (S-thionylation, i.e. in particularS-glutathionylation,S-cysteinylglycinylation andS-cysteinylation). A wide array of proteins have been thus analyzed in detail as far as their susceptibility to either modification or both, and the resulting functional changes have been described in a number of experimental settings. The present review aims to provide an update of available knowledge in the field, with a special focus on the respective (sometimes competing and antagonistic) roles played by proteinS-nitrosations andS-thionylations in biochemical and cellular processes specifically pertaining to pathogenesis of cardiovascular diseases.

Potential therapeutic action of nitrite in sickle cell disease

Sickle cell disease is caused by a mutant form of hemoglobin that polymerizes under hypoxic conditions, increasing rigidity, fragility, calcium influx-mediated dehydration, and adhesivity of red blood cells. Increased red cell fragility results in hemolysis, which reduces nitric oxide (NO) bioavailability, and induces platelet activation and inflammation leading to adhesion of circulating blood cells. Nitric Oxide inhibits adhesion and platelet activation. Nitrite has emerged as an attractive therapeutic agent that targets delivery of NO activity to areas of hypoxia through bioactivation by deoxygenated red blood cell hemoglobin. In this study, we demonstrate anti-platelet activity of nitrite at doses achievable through dietary interventions with comparison to similar doses with other NO donating agents. Unlike other NO donating agents, nitrite activity is shown to be potentiated in the presence of red blood cells in hypoxic conditions. We also show that nitrite reduces calcium associated loss of phospholipid asymmetry that is associated with increased red cell adhesion, and that red cell deformability is also improved. We show that nitrite inhibits red cell adhesion in a microfluidic flow-channel assay after endothelial cell activation. In further investigations, we show that leukocyte and platelet adhesion is blunted in nitrite-fed wild type mice compared to control after either lipopolysaccharide- or hemolysis-induced inflammation. Moreover, we demonstrate that nitrite treatment results in a reduction in adhesion of circulating blood cells and reduced red blood cell hemolysis in humanized transgenic sickle cell mice subjected to local hypoxia. These data suggest that nitrite is an effective anti-platelet and anti-adhesion agent that is activated by red blood cells, with enhanced potency under physiological hypoxia and in venous blood that may be useful therapeutically.

Vascular nitric oxide: Beyond eNOS

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

S-nitrosoglutathione reduces tau hyper-phosphorylation and provides neuroprotection in rat model of chronic cerebral hypoperfusion

We have previously reported that treatment of rats subjected to permanent bilateral common carotid artery occlusion (pBCCAO), a model of chronic cerebral hypoperfusion (CCH), with S-nitrosoglutathione (GSNO), an endogenous nitric oxide carrier, improved cognitive functions and decreased amyloid-β accumulation in the brains. Since CCH has been implicated in tau hyperphosphorylation induced neurodegeneration, we investigated the role of GSNO in regulation of tau hyperphosphorylation in rat pBCCAO model. The rats subjected to pBCCAO had a significant increase in tau hyperphosphorylation with increased neuronal loss in hippocampal/cortical areas. GSNO treatment attenuated not only the tau hyperphosphorylation, but also the neurodegeneration in pBCCAO rat brains. The pBCCAO rat brains also showed increased activities of GSK-3β and Cdk5 (major tau kinases) and GSNO treatment significantly attenuated their activities. GSNO attenuated the increased calpain activities and calpain-mediated cleavage of p35 leading to production of p25 and aberrant Cdk5 activation. In in vitro studies using purified calpain protein, GSNO treatment inhibited calpain activities while 3-morpholinosydnonimine (a donor of peroxynitrite) treatment increased its activities, suggesting the opposing role of GSNO vs. peroxynitrite in regulation of calpain activities. In pBCCAO rat brains, GSNO treatment attenuated the expression of inducible nitric oxide synthase (iNOS) expression and also reduced the brain levels of nitro-tyrosine formation, thereby indicating the protective role of GSNO in iNOS/nitrosative-stress mediated calpain/tau pathologies under CCH conditions. Taken together with our previous report, these data support the therapeutic potential of GSNO, a biological NO carrier, as a neuro- and cognitive-protective agent under conditions of CCH.

S-Nitrosoglutathione improves haemodynamics in early-onset pre-eclampsia

AIMS

To determine the effects of in vivo S-nitrosoglutathione (GSNO) infusion on cardiovascular function, platelet function, proteinuria and biomarker parameters in early-onset pre-eclampsia.

METHODS

We performed an open-label dose-ranging study of GSNO in early-onset pre-eclampsia. Six women underwent GSNO infusion whilst receiving standard therapy. The dose of GSNO was increased incrementally to 100 μg min(-1) whilst maintaining blood pressure of >140/80 mmHg. Aortic augmentation index, aortic pulse wave velocity, blood pressure and maternal-fetal Doppler parameters were measured at each dose. Platelet P-selectin, protein-to-creatinine ratio and soluble anti-angiogenic factors were measured pre- and postinfusion.

RESULTS

Augmentation index fell at 30 μg min(-1) S-nitrosoglutathione (-6%, 95% confidence interval 0.6 to 13%), a dose that did not affect blood pressure. Platelet P-selectin expression was reduced [mean (interquartile range), 6.3 (4.9-7.6) vs. 4.1 (3.1-5.7)% positive, P = 0.03]. Soluble endoglin levels showed borderline reduction (P = 0.06). There was a borderline significant change in pre-to-postinfusion protein-to-creatinine ratio [mean (interquartile range), 0.37 (0.09-0.82) vs. 0.23 (0.07-0.49) g mmol(-1) , P = 0.06]. Maternal uterine and fetal Doppler pulsatility indices were unchanged.

CONCLUSIONS

In early-onset pre-eclampsia, GSNO reduces augmentation index, a biomarker of small vessel tone and pulse wave reflection, prior to affecting blood pressure. Proteinuria and platelet activation are improved at doses that affect blood pressure minimally. These effects of GSNO may be of therapeutic potential in pre-eclampsia, a condition for which no specific treatment exists. Clinical studies of GSNO in early-onset pre-eclampsia will determine whether these findings translate to improvement in maternal and/or fetal outcome.

The nitric oxide pathway and possible therapeutic options in pre-eclampsia

Pre-eclampsia is a serious multisystem disorder with diverse clinical manifestations. Although not causal, endothelial dysfunction and reduced nitric oxide bioavailability are likely to play an important role in the maternal and fetal pathophysiology of this condition. Lack of treatment modalities that can target the underlying pathophysiological changes and reverse the endothelial dysfunction frequently leads to iatrogenic preterm delivery of the fetus, causing neonatal morbidity and mortality, and the condition itself is associated with short- and longer term maternal morbidity and mortality. Drugs that target various components of the nitric oxide-soluble guanylyl cyclase pathway can help to increase NO bioavailability. The purpose of this review is to outline the current status of clinical research involving these therapeutic modalities in the context of pre-eclampsia, with the focus being on the following: nitric oxide donors, including organic nitrates and S-nitrosothiols; l-arginine, the endogenous precursor of NO; inhibitors of cyclic guanosine 3',5'-monophosphate breakdown, including sildenafil; and other novel inhibitors of NO donor metabolism. The advantages and limitations of each modality are outlined, and scope for development into established therapeutic options for pre-eclampsia is explored.

Time lasting S-nitrosoglutathione polymeric nanoparticles delay cellular protein S-nitrosation

Physiological S-nitrosothiols (RSNO), such as S-nitrosoglutathione (GSNO), can be used as nitric oxide (NO) donor for the treatment of vascular diseases. However, despite a half-life measured in hours, the stability of RSNO, limited by enzymatic and non-enzymatic degradations, is too low for clinical application. So, to provide a long-lasting effect and to deliver appropriate NO concentrations to target tissues, RSNO have to be protected. RSNO encapsulation is an interesting response to overcome degradation and provide protection. However, RSNO such as GSNO raise difficulties for encapsulation due to its hydrophilic nature and the instability of the S-NO bound during the formulation process. To our knowledge, the present study is the first description of the direct encapsulation of GSNO within polymeric nanoparticles (NP). The GSNO-loaded NP (GSNO-NP) formulated by a double emulsion process, presented a mean diameter of 289 ± 7 nm. They were positively charged (+40 mV) due to the methacrylic acid and ethylacrylate polymer (Eudragit® RL) used and encapsulated GSNO with a satisfactory efficiency (i.e. 54% or 40 mM GSNO loaded in the NP). In phosphate buffer (37 °C; pH 7.4), GSNO-NP released 100% of encapsulated GSNO within 3h and remained stable still 6h. However, in contact with smooth muscle cells, maximum protein nitrosation (a marker of NO bioavailability) was delayed from 1h for free GSNO to 18h for GSNO-NP. Therefore, protection and sustained release of NO were achieved by the association of a NO donor with a drug delivery system (such as polymeric NP), providing opportunities for vascular diseases treatment.

Protective role of S-nitrosoglutathione (GSNO) against cognitive impairment in rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH), featuring in most of the Alzheimer's disease spectrum, plays a detrimental role in brain amyloid-β (Aβ) homeostasis, cerebrovascular morbidity, and cognitive decline; therefore, early management of cerebrovascular pathology is considered to be important for intervention in the impending cognitive decline. S-nitrosoglutathione (GSNO) is an endogenous nitric oxide carrier modulating endothelial function, inflammation, and neurotransmission. Therefore, the effect of GSNO treatment on CCH-associated neurocognitive pathologies was determined in vivo by using rats with permanent bilateral common carotid artery occlusion (BCCAO), a rat model of chronic cerebral hypoperfusion. We observed that rats subjected to permanent BCCAO showed a significant decrease in learning/memory performance and increases in brain levels of Aβ and vascular inflammatory markers. GSNO treatment (50 μg/kg/day for 2 months) significantly improved learning and memory performance of BCCAO rats and reduced the Aβ levels and ICAM-1/VCAM-1 expression in the brain. Further, in in vitro cell culture studies, GSNO treatment also decreased the cytokine-induced proinflammatory responses, such as activations of NFκB and STAT3 and expression of ICAM-1 and VCAM-1 in endothelial cells. In addition, GSNO treatment increased the endothelial and microglial Aβ uptake. Additionally, GSNO treatment inhibited the β-secretase activity in primary rat neuron cell culture, thus reducing secretion of Aβ, suggesting GSNO mediated mechanisms in anti-inflammatory and anti-amyloidogenic activities. Taken together, these data document that systemic GSNO treatment is beneficial for improvement of cognitive decline under the conditions of chronic cerebral hypoperfusion and suggests a potential therapeutic use of GSNO for cerebral hypoperfusion associated mild cognitive impairment in Alzheimer's disease.

Long-term nitric oxide release and elevated temperature stability with S-nitroso-N-acetylpenicillamine (SNAP)-doped Elast-eon E2As polymer

Nitric oxide (NO) is known to be a potent inhibitor of platelet activation and adhesion. Healthy endothelial cells that line the inner walls of all blood vessels exhibit a NO flux of 0.5-4 × 10(-10) mol cm(-2) min(-1) that helps prevent thrombosis. Materials with a NO flux that is equivalent to this level are expected to exhibit similar anti-thrombotic properties. In this study, five biomedical grade polymers doped with S-nitroso-N-acetylpenicillamine (SNAP) were investigated for their potential to control the release of NO from the SNAP within the polymers, and further control the release of SNAP itself. SNAP in the Elast-eon E2As polymer creates an inexpensive, homogeneous coating that can locally deliver NO (via thermal and photochemical reactions) as well slowly release SNAP. Furthermore, SNAP is surprisingly stable in the E2As polymer, retaining 82% of the initial SNAP after 2 months storage at 37 °C. The E2As polymer containing SNAP was coated on the walls of extracorporeal circulation (ECC) circuits and exposed to 4 h blood flow in a rabbit model of extracorporeal circulation to examine the effects on platelet count, platelet function, clot area, and fibrinogen adsorption. After 4 h, platelet count was preserved at 100 ± 7% of baseline for the SNAP/E2As coated loops, compared to 60 ± 6% for E2As control circuits (n = 4). The SNAP/E2As coating also reduced the thrombus area when compared to the control (2.3 ± 0.6 and 3.4 ± 1.1 pixels/cm(2), respectively). The results suggest that the new SNAP/E2As coating has potential to improve the thromboresistance of intravascular catheters, grafts, and other blood-contacting medical devices, and exhibits excellent storage stability compared to previously reported NO release polymeric materials.

S-nitrosoglutathione

BACKGROUND

S-Nitrosoglutathione (GSNO) is the S-nitrosated derivative of glutathione and is thought to be a critical mediator of the down stream signaling effects of nitric oxide (NO). GSNO has also been implicated as a contributor to various disease states.

SCOPE OF REVIEW

This review focuses on the chemical nature of GSNO, its biological activities, the evidence that it is an endogenous mediator of NO action, and implications for therapeutic use.

MAJOR CONCLUSIONS

GSNO clearly exerts its cellular actions through both NO- and S-nitrosation-dependent mechanisms; however, the chemical and biological aspects of this compound should be placed in the context of S-nitrosation as a whole.

GENERAL SIGNIFICANCE

GSNO is a central intermediate in formation and degradation of cellular S-nitrosothiols with potential therapeutic applications; thus, it remains an important molecule of study. This article is part of a Special Issue entitled Cellular functions of glutathione.

Nitroglycerin and sodium nitroprusside: potential contributors to postoperative bleeding?

Postoperative bleeding is common in patients undergoing cardiac surgery with cardiopulmonary bypass. Most cases of severe postoperative bleeding not due to incomplete surgical hemostasis are related to acquired transient platelet dysfunction mediated by platelet activation during contact with the synthetic surfaces of the cardiopulmonary bypass equipment. Antihypertensive agents nitroglycerin and sodium nitroprusside have been shown to have platelet inhibitory properties, yet the clinical consequence in terms of postoperative bleeding has been little studied. Knowing that cardiopulmonary bypass causes platelet dysfunction, it is prudent for physicians to be aware of the additional platelet inhibition caused by these commonly used antihypertensive agents.

Optimization of cardiovascular stent against restenosis: factorial design-based statistical analysis of polymer coating conditions

The objective of this study was to optimize the physicodynamic conditions of polymeric system as a coating substrate for drug eluting stents against restenosis. As Nitric Oxide (NO) has multifunctional activities, such as regulating blood flow and pressure, and influencing thrombus formation, a continuous and spatiotemporal delivery of NO loaded in the polymer based nanoparticles could be a viable option to reduce and prevent restenosis. To identify the most suitable carrier for S-Nitrosoglutathione (GSNO), a NO prodrug, stents were coated with various polymers, such as poly (lactic-co-glycolic acid) (PLGA), polyethylene glycol (PEG) and polycaprolactone (PCL), using solvent evaporation technique. Full factorial design was used to evaluate the effects of the formulation variables in polymer-based stent coatings on the GSNO release rate and weight loss rate. The least square regression model was used for data analysis in the optimization process. The polymer-coated stents were further assessed with Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy analysis (FTIR), Scanning electron microscopy (SEM) images and platelet adhesion studies. Stents coated with PCL matrix displayed more sustained and controlled drug release profiles than those coated with PLGA and PEG. Stents coated with PCL matrix showed the least platelet adhesion rate. Subsequently, stents coated with PCL matrix were subjected to the further optimization processes for improvement of surface morphology and enhancement of the drug release duration. The results of this study demonstrated that PCL matrix containing GSNO is a promising system for stent surface coating against restenosis.

S-nitrosoglutathione acts as a small molecule modulator of human fibrin clot architecture

BACKGROUND

Altered fibrin clot architecture is increasingly associated with cardiovascular diseases; yet, little is known about how fibrin networks are affected by small molecules that alter fibrinogen structure. Based on previous evidence that S-nitrosoglutathione (GSNO) alters fibrinogen secondary structure and fibrin polymerization kinetics, we hypothesized that GSNO would alter fibrin microstructure.

METHODOLOGY/PRINCIPAL FINDINGS

Accordingly, we treated human platelet-poor plasma with GSNO (0.01-3.75 mM) and imaged thrombin induced fibrin networks using multiphoton microscopy. Using custom designed computer software, we analyzed fibrin microstructure for changes in structural features including fiber density, diameter, branch point density, crossing fibers and void area. We report for the first time that GSNO dose-dependently decreased fibrin density until complete network inhibition was achieved. At low dose GSNO, fiber diameter increased 25%, maintaining clot void volume at approximately 70%. However, at high dose GSNO, abnormal irregularly shaped fibrin clusters with high fluorescence intensity cores were detected and clot void volume increased dramatically. Notwithstanding fibrin clusters, the clot remained stable, as fiber branching was insensitive to GSNO and there was no evidence of fiber motion within the network. Moreover, at the highest GSNO dose tested, we observed for the first time, that GSNO induced formation of fibrin agglomerates.

CONCLUSIONS/SIGNIFICANCE

Taken together, low dose GSNO modulated fibrin microstructure generating coarse fibrin networks with thicker fibers; however, higher doses of GSNO induced abnormal fibrin structures and fibrin agglomerates. Since GSNO maintained clot void volume, while altering fiber diameter it suggests that GSNO may modulate the remodeling or inhibition of fibrin networks over an optimal concentration range.

The molecular design of S-nitrosothiols as photodynamic agents for controlled nitric oxide release

Nitric oxide is a small messenger molecule utilized by nature in cell signalling and the non-specific immune response. At present, nitric oxide releasing prodrugs cannot be efficiently targeted towards a specific body compartment, which restricts their therapeutic applications. To address this limitation, we have designed two photolabile nitric oxide releasing prodrugs, tert-butyl S-nitrosothiol and tert-dodecane S-nitrosothiol, which are based on the S-nitrosothiol functionality. By modulating the prodrugs' hydrophobicity, we postulated that we could increase their stability within the cell by preventing their interaction with hydrophilic thiols and metal ions; processes that are known to inactivate this prodrug class. Our data demonstrate that these prodrugs have improved nitric oxide release kinetics compared to currently available S-nitrosothiols, as they are highly stable in vitro in the absence of irradiation (t(1/2) > 3 h), while their rate of decomposition can be regulated by controlling the intensity or duration of the photostimulus. Nitric oxide release can readily be achieved using non-laser based light sources, which enabled us to characterize photoactivation as a trigger mechanism for nitric oxide release in A549 lung carcinoma cells. Here we confirmed that irradiation induced highly significant increases in cytotoxicity within a therapeutic drug range (1-100 μm), and the utility of this photoactivation switch opens up avenues for exploring the applications of these prodrugs for chemical biology studies and chemotherapy.

A nanoparticle delivery vehicle for S-nitroso-N-acetyl cysteine: sustained vascular response

Interest in the development of nitric oxide (NO) based therapeutics has grown exponentially due to its well elucidated and established biological functions. In line with this surge, S-nitroso thiol (RSNO) therapeutics are also receiving more attention in recent years both as potential stable sources of NO as well as for their ability to serve as S-nitrosating agents; S-nitrosation of protein thiols is implicated in many physiological processes. We describe two hydrogel based RSNO containing nanoparticle platforms. In one platform the SNO groups are covalently attached to the particles (SNO-np) and the other contains S-nitroso-N-acetyl cysteine encapsulated within the particles (NAC-SNO-np). Both platforms function as vehicles for sustained activity as trans-S-nitrosating agents. NAC-SNO-np exhibited higher efficiency for generating GSNO from GSH and maintained higher levels of GSNO concentration for longer time (24 h) as compared to SNO-np as well as a previously characterized nitric oxide releasing platform, NO-np (nitric oxide releasing nanoparticles). In vivo, intravenous infusion of the NAC-SNO-np and NO-np resulted in sustained decreases in mean arterial pressure, though NAC-SNO-np induced longer vasodilatory effects as compared to the NO-np. Serum chemistries following infusion demonstrated no toxicity in both treatment groups. Together, these data suggest that the NAC-SNO-np represents a novel means to both study the biologic effects of nitrosothiols and effectively capitalize on its therapeutic potential.

Stöber Synthesis of Nitric Oxide-Releasing S-Nitrosothiol-Modified Silica Particles

We report the synthesis of S-nitrosothiol-modified silica particles capable of nitric oxide (NO) release. The thiol precursor modification to form S-nitrosothiol NO donors was introduced into the silica network via co-condensation of mercaptosilane and alkoxysilane precursors. Both the concentrations of reactants (i.e., water, ammonia, and silane) and the silane feed rate into the reaction proved important in the yield of monodisperse, spherical particles with tunable diameters ranging from 241-718 nm. Subsequent nitrosation resulted in NO storage approaching ~4.40 μmol NO mg(-1), as determined by total NO release. Behaving similar to low molecular weight S-nitrosothiol NO donors, the NO release from the macromolecular silica vehicles was influenced by light, temperature, and metal ions.

Endothelin attenuates endothelium-dependent platelet inhibition in man

AIM

The vascular endothelium produces several substances, including nitric oxide (NO) and endothelin-1 (ET-1), which participate in the regulation of vascular tone in humans. Both these substances may exert other actions of importance for cardiovascular disease, e.g. effects on vascular smooth muscle cell proliferation and inflammation, and NO inhibits platelet function. Experiments were designed to investigate the effect of ET-1 on endothelium-dependent vasodilatation and attenuation of platelet activation.

METHODS

In 25 healthy male subjects (25 +/- 1 years), forearm blood flow was measured by venous occlusion plethysmography, and platelet activity was assessed by whole blood flow cytometry (platelet fibrinogen binding and P-selectin expression) in unstimulated and adenosine diphosphate (ADP)-stimulated samples during administration of ET-1, the endothelium-dependent vasodilator acetylcholine and the NO synthase inhibitor l-NMMA.

RESULTS

Acetylcholine increased forearm blood flow and significantly inhibited platelet activation in both unstimulated and ADP-stimulated samples. In samples stimulated with 0.3 microm ADP, fibrinogen binding decreased from 41 +/- 4% to 31 +/- 3% (P < 0.01, n = 11) after acetylcholine administration. The vasodilator response to acetylcholine was significantly impaired during infusions of ET-1 and l-NMMA. ET-1 did not affect platelet activity per se, whereas l-NMMA increased platelet P-selectin expression. Both ET-1 and l-NMMA attenuated the acetylcholine-induced inhibition of platelet activity.

CONCLUSIONS

Our study indicates that, further to inhibiting endothelium-dependent vasodilatation, ET-1 may also attenuate endothelium-dependent inhibition of platelet activation induced by acetylcholine. An enhanced ET-1 activity, as suggested in endothelial dysfunction, may affect endothelium-dependent platelet modulation and thereby have pathophysiological implications.

Nitric oxide-releasing S-nitrosothiol-modified xerogels

The synthesis, material characterization, and in vitro biocompatibility of S-nitrosothiol (RSNO)-modified xerogels are described. Thiol-functionalized xerogel films were formed by hydrolysis and co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and methyltrimethoxysilane (MTMOS) sol-gel precursors at varying concentrations. Subsequent thiol nitrosation via acidified nitrite produced RSNO-modified xerogels capable of generating nitric oxide (NO) for up to 2 weeks under physiological conditions. Xerogels also exhibited NO generation upon irradiation with broad-spectrum light or exposure to copper, with NO fluxes proportional to wattage and concentration, respectively. Xerogels were capable of storing up to approximately 1.31 micromol NO mg(-1), and displayed negligible fragmentation over a 2-week period. Platelet and bacterial adhesion to nitrosated films was reduced compared to non-nitrosated controls, confirming the antithrombotic and antibacterial properties of the NO-releasing materials. Fibroblast cell viability was maintained on the xerogel surfaces illustrating the promise of RSNO-modified xerogels as biomedical device coatings.

Is there a rationale for the chronic use of phosphodiesterase-5 inhibitors for lower urinary tract symptoms secondary to benign prostatic hyperplasia?

OBJECTIVES

To critically review the physiological roles of phosphodiesterase-5 (PDE5), to explain and support the putative impact and clinical significance of PDE5 inhibitors (PDE5-Is) in the treatment of lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) and erectile dysfunction (ED), both highly prevalent in men aged > or =50 years, as PDE5-Is are very effective as a first-line therapy for ED, and attractive for further physiological functional investigations.

METHODS

We searched Medline for peer-reviewed articles in English, from 1991 to 2008, to provide a critical contemporary review of PDE5 pertaining to the potential interest of findings supporting a role for PDE5-Is in LUTS due to BPH. The selection of papers was based on the relevance of subject matter. A critical analysis of available fundamental and clinical data is reported.

RESULTS

Several studies assessed the role of the nitric oxide/cGMP signalling pathway in the regulation of the prostate tone, with the support of clinical observations. PDE5-Is can also represent a potential mode of action allowing the targeting of transcriptional activity implicated in the regulation of the progression of the inflammatory process involved in BPH. PDE5-Is can inhibit human stromal cell proliferation of the prostate mediated by cGMP accumulation. New targeting hypotheses of pathophysiological processes are also reported.

CONCLUSIONS

There is evidence that LUTS and ED are strongly linked. This analysis of the regulatory basis of PDE5 biology could indicate several directions of investigation. However, it is necessary to devise well-designed large prospective studies that would produce significant data before this approach becomes a standard of care.

Attenuated severity of new acute ischemic events in patients with previous coronary heart disease receiving long-acting nitrates

BACKGROUND

Platelet aggregation and secondary vasoconstriction are key events in the genesis of acute coronary syndromes.

HYPOTHESIS

Since nitrates have vasodilatory and antiaggregant effects, treatment with long-acting nitrates at the time of onset of acute coronary syndromes could be associated with attenuation of their severity.

METHODS

A consecutive series of 533 patients with acute coronary syndrome and past history of coronary artery disease admitted to the Cardiology Service of a general hospital was studied. A specific questionnaire assessed the use of nitrates and other relevant drugs, as well as other clinical variables. The diagnosis of unstable angina or acute myocardial infarction (MI) was established according to clinical, electrocardiographic, and enzymatic criteria.

RESULTS

In the whole cohort, 169 patients had MI and 364 had unstable angina. Previous use of long-acting nitrates was significantly more common in patients with unstable angina (56%) than in those with MI (37%) (p < 0.0001). Multivariate analysis identified being a nonsmoker [odds ratio: 95%, confidence limits (CL) 0.37, 0.23-0.59], previous unstable angina (CL 0.62, 0.41-0.92), use of aspirin (CL 0.58, 0.41-0.92), and use of long-acting nitrates (CL 0.61, 0.40-0.93) as the independent predictors of the development of unstable angina rather than MI; of these the combination of nitrates and aspirin was the strongest predictor.

CONCLUSIONS

Long-acting nitrates as well as aspirin are suggested to have a protective or modifying effect on the development of acute coronary syndromes, favoring unstable angina rather than acute MI.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

The vascular endothelium of the coronary arteries has been identified as the important organ that locally regulates coronary perfusion and cardiac function by paracrine secretion of nitric oxide (NO) and vasoactive peptides. NO is constitutively produced in endothelial cells by endothelial nitric oxide synthase (eNOS). NO derived from this enzyme exerts important biological functions including vasodilatation, scavenging of superoxide and inhibition of platelet aggregation. Routine cardiac surgery or cardiologic interventions lead to a serious temporary or persistent disturbance in NO homeostasis. The clinical consequences are "endothelial dysfunction", leading to "myocardial dysfunction": no- or low-reflow phenomenon and temporary reduction of myocardial pump function. Uncoupling of eNOS (one electron transfer to molecular oxygen, the second substrate of eNOS) during ischemia-reperfusion due to diminished availability of L-arginine and/or tetrahydrobiopterin is even discussed as one major source of superoxide formation. Therefore maintenance of normal NO homeostasis seems to be an important factor protecting from ischemia/reperfusion (I/R) injury. Both, the clinical situations of cardioplegic arrest as well as hypothermic cardioplegic storage are followed by reperfusion. However, the presently used cardioplegic solutions to arrest and/or store the heart, thereby reducing myocardial oxygen consumption and metabolism, are designed to preserve myocytes mainly and not endothelial cells. This review will focus on possible drug additives to cardioplegia, which may help to maintain normal NO homeostasis after I/R.

S-nitrosoglutathione-containing hydrogel accelerates rat cutaneous wound repair

BACKGROUND

Nitric oxide (NO) plays a key role in wound repair and S-nitrosothiols like S-nitrosoglutathione (GSNO) are well known NO donors.

METHODS

Animals were separated in two groups and submitted to excisional wounds on the dorsal surface at the first day. GSNO (100 microm)-containing hydrogels were topically applied on the wound bed in the GSNO group, daily, during the first 4 days. Control group was topically treated with hydrogel without GSNO for the same period. Wound contraction and re-epithelialization were measured. Animals were sacrificed 21 days after wounding. Samples of lesion and normal tissue were formalin-fixed, paraffin embedded for histological analysis.

RESULTS

Wound contraction, measured 14 and 21 days after wounding, was greater in the GSNO group than in the control group (P<0.05 for both). The re-epithelialized wound area, measured 14 days after wounding, was higher in the GSNO group than in the control group (P<0.05). A higher amount of inflammatory cells was observed in superficial and deep areas of the granulation tissue of the control group compared to the GSNO group. Twenty-one days after wounding, thin red-yellow collagen fibers arranged perpendicularly to the surface were found in the granulation tissue of the control group, whereas in the GSNO-treated group collagen fibers were thicker and arranged parallel to the surface. Increased number of mast cells was observed in the GSNO group compared with that in the control group. Vascularization and myofibroblast distribution were similar in both groups.

CONCLUSION

Topical application of GSNO-containing hydrogel during the early phases of rat cutaneous wound repair accelerates wound closure and re-epithelialization and affects granulation tissue organization.

Recent developments in nitric oxide donor drugs

During the 1980s, the free radical, nitric oxide (NO), was discovered to be a crucial signalling molecule, with wide-ranging functions in the cardiovascular, nervous and immune systems. Aside from providing a credible explanation for the actions of organic nitrates and sodium nitroprusside that have long been used in the treatment of angina and hypertensive crises respectively, the discovery generated great hopes for new NO-based treatments for a wide variety of ailments. Decades later, however, we are still awaiting novel licensed agents in this arena, despite an enormous research effort to this end. This review explores some of the most promising recent advances in NO donor drug development and addresses the challenges associated with NO as a therapeutic agent.

Flavanols and Cardiovascular Health: Effects on the circulating NO Pool in Humans

Atherosclerosis is the major cause for chronic vascular diseases. The key event in the pathogenesis of atherosclerosis is believed to be dysfunction of the endothelium and disruption of endothelial homeostasis, leading to vasoconstriction, inflammation, leukocyte adhesion, thrombosis, and proliferation of vascular smooth muscle cells. Endothelium-derived nitric oxide (NO) plays a major role in vascular homeostasis and a decrease in NO-bioavailability accelerates the development of atherosclerosis. Given that endothelial dysfunction is at least in part reversible, the characterization of endothelial function and therapeutical approaches have gained much attention over the past years. Recent studies demonstrated that especially the consumption of plant-derived foods rich in certain flavonoids can improve endothelial function in both compromised and healthy humans. Furthermore, various physiologic and biochemical measures have been used previously as biomarkers for the assessment of the proposed beneficial effects of flavonoids in this context. More recently, the analysis of plasma nitros(yl)ated species (RXNOs), referred to as the circulating NO pool, has gained recognition, especially as a marker for endothelial function. This review is aimed at evaluating the suitability of quantifying this NO pool as a biomarker for cardiovascular function in humans, in particular during dietary interventions with flavonoid-rich foods.

Plasma nitroso compounds are decreased in patients with endothelial dysfunction

OBJECTIVES

We investigated whether plasma nitros(yl)ated species (RXNOs) that mediate systemic nitric oxide (NO) bioactivity are depleted in individuals with cardiovascular risk factors and endothelial dysfunction.

BACKGROUND

Endothelium-derived NO acts not only as a regional messenger but exerts significant systemic effects via formation of circulating RXNOs delivering NO to sites of impaired production.

METHODS

Endothelial function was assessed in 68 patients with one to four major cardiovascular risk factors (RF) and 39 healthy control subjects (C) by measurement of flow-mediated dilation (FMD) of the brachial artery using high-resolution ultrasound. In parallel, plasma RXNOs were determined by reductive gas phase chemiluminescence.

RESULTS

Increasing numbers of risk factors were accompanied by a progressive decrease in FMD: 6.5 +/- 0.4% (C); 4.7 +/- 0.5% (one RF); 2.8 +/- 0.4% (two RF); 2.2 +/- 0.4% (three RF); and 1.0 +/- 0.3% (four RF). Progressively impaired vascular function was associated with a concomitant decrease in plasma RXNOs (p < 0.01): 39 +/- 2 nmol/l (C); 30 +/- 2 nmol/l (one RF); 24 +/- 3 nmol/l (two RF); 22 +/- 3 nmol/l (three RF); and 15 +/- 2 nmol/l (four RF), with univariate correlation between FMD and RXNO (r = 0.41, p < 0.001). In a multivariate regression model, RXNO was an independent predictor of endothelial function.

CONCLUSIONS

Endothelial dysfunction in patients with cardiovascular risk factors is associated with decreased levels of circulating RXNOs. Plasma RXNOs may be diagnostically useful markers of NO bioavailability and a surrogate index of endothelial function. Whether the observed decrease in concentration reflects impaired NO formation, accelerated decomposition, and/or consumption of RXNOs and whether these processes play a causal role in the pathophysiology of arteriosclerosis remain to be investigated.