Prevention of pulmonary thromboembolism by NCX 4016, a nitric oxide-releasing aspirin

Gaseous Mediators as a Key Molecular Targets for the Development of Gastrointestinal-Safe Anti-Inflammatory Pharmacology

Non-steroidal anti-inflammatory drugs (NSAIDs) represent one of the most widely used classes of drugs and play a pivotal role in the therapy of numerous inflammatory diseases. However, the adverse effects of these drugs, especially when applied chronically, frequently affect gastrointestinal (GI) tract, resulting in ulceration and bleeding, which constitutes a significant limitation in clinical practice. On the other hand, it has been recently discovered that gaseous mediators nitric oxide (NO), hydrogen sulfide (H2S) and carbon monoxide (CO) contribute to many physiological processes in the GI tract, including the maintenance of GI mucosal barrier integrity. Therefore, based on the possible therapeutic properties of NO, H2S and CO, a novel NSAIDs with ability to release one or more of those gaseous messengers have been synthesized. Until now, both preclinical and clinical studies have shown promising effects with respect to the anti-inflammatory potency as well as GI-safety of these novel NSAIDs. This review provides an overview of the gaseous mediators-based NSAIDs along with their mechanisms of action, with special emphasis on possible implications for GI mucosal defense mechanisms.

Treatment with new organic nitrites in pulmonary hypertension of acute experimental pulmonary embolism

Acute pulmonary embolism may cause right heart failure due to increased pulmonary vascular resistance and arterial hypoxemia. Effective vasodilator therapy of the pulmonary hypertension is highly needed. Therefore, we investigated the effects of a newly developed effective pulmonary vasodilator, the organic mononitrites of 1,2-propanediol (PDNO), in a rabbit model of acute pulmonary embolism. In anesthetized and ventilated rabbits, systemic and pulmonary hemodynamics, exhaled nitric oxide (NO), plasma nitrite concentration, and blood gases were monitored. First, dose-response experiments with intravenous and left heart ventricle infusions of PDNO and inorganic nitrite were done in naive animals and in pulmonary hypertension induced by a thromboxane A2 analogue. Second, acute pulmonary embolism was induced and either PDNO or placebo were administered intravenously within 20 minutes and evaluated within 1 hour after pulmonary embolization. PDNO intravenously, in contrast to inorganic nitrite intravenously, increased exhaled NO and counteracted pulmonary hypertension and vasodilated the systemic circulation, dose-dependently, thereby showing efficient NO donation. Pulmonary embolization induced pulmonary hypertension and gas exchange disturbances. PDNO significantly decreased and normalized pulmonary vascular resistance and the right ventricle rate-pressure product, without causing tolerance, with no significant side effects on the systemic circulation, nor on blood-gas values or on methemoglobin formation. In conclusion, PDNO is a NO donor and an efficient vasodilator in the pulmonary circulation. Treatment with this or similar organic nitrites intravenously may be a future option to avoid right heart failure in life-threatening acute pulmonary embolism.

Refinement of a mouse cardiovascular model: Development, application and dissemination

European and UK legislation requires all animal procedures to be conducted with consideration to reduction, refinement and replacement. In this review, 3Rs developments are discussed in the field of platelet biology and thromboembolism. Platelet research requires the use of animal models, and mice are widely used in the field. When working in vitro, conventional light transmission techniques have been scaled down allowing reduction in animal numbers. In vivo, vascular injury models are widely used and work is ongoing to develop ex vivo approaches that use fewer animals. Thromboembolic mortality models, which inflict considerable pain and suffering, have also been used widely. A published and characterised refinement of this mortality model allows real-time monitoring of radiolabelled platelets under general anaesthesia and reduces both the severity level and the numbers of mice used in a typical experiment. This technique is more sensitive than the mortality approach and has opened up new avenues of research, which would not have been feasible by using death as an end-point. To drive uptake of real-time monitoring, a more simplistic approach has been developed involving micro-sampling and cell counting. Thromboembolic mortality models should therefore be considered obsolete due to the emergence of 3Rs models with improved scientific outcomes and that can be implemented relatively easily.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

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.

Stimulation of platelet nitric oxide production by nebivolol prevents thrombosis

OBJECTIVE

dl-Nebivolol, a selective β1-adrenergic receptor antagonist, besides its hypotensive activity exerts vasodilatory and platelet inhibitory effects in vitro by a mechanism involving nitric oxide (NO). Our aim was to evaluate whether nebivolol exerts in vivo antithrombotic effects, to unravel the mechanism of this action and to clarify the relative roles of its 2 enantiomers: d- and l-nebivolol.

METHODS AND RESULTS

In wild-type mice, dl-nebivolol, l-nebivolol, and d-nebivolol, but not bisoprolol, reduced mortality consequent to platelet pulmonary thromboembolism induced by the intravenous injection of collagen plus epinephrine (-44%, -45%, -29%, respectively; P<0.05), whereas in eNOS(-/-) mice only dl-nebivolol and d-nebivolol were effective. dl-Nebivolol, l- and d-nebivolol reduced photochemical damage-induced femoral artery thrombosis in wild-type mice, whereas in eNOS(-/-) mice only dl-nebivolol and d-nebivolol were active. Moreover, dl-nebivolol and l-nebivolol increased plasma, urinary-, and platelet-derived nitrites and nitrates (NOx), NO degradation products, in wild-type but not in eNOS(-/-) mice. In vivo platelet activation, assessed by platelet P-selectin expression, was reduced by dl-nebivolol and l- and d-nebivolol in wild-type mice but only by dl-nebivolol and d-nebivolol in eNOS(-/-) mice. In bone marrow-transplanted, chimeric mice with only blood cells, and not the endothelium, producing NO dl-nebivolol and l-nebivolol maintained their antithrombotic activity, whereas they lose it in chimeras with only endothelium, and not blood cells, producing NO. In vitro, with isolated platelets, dl-nebivolol and l-nebivolol, but not d-nebivolol and bisoprolol, increased platelet cGMP and NOx formation. Treatment with dl-nebivolol and l-nebivolol increased phophorylated eNOS in platelets.

CONCLUSIONS

Our data show that dl-nebivolol exerts an antithrombotic activity by stimulating the formation of NO by platelets, and that this effect is generated by its l-enantiomer, whereas the d-enantiomer exerts a weak antiplatelet effect because of β-adrenergic receptor-independent stimulation of adenyly cyclase. These results confirm that platelet-derived NO plays a role in thrombosis prevention and it may represent a target of pharmacological intervention.

NO-donating aspirin and aspirin partially inhibit age-related atherosclerosis but not radiation-induced atherosclerosis in ApoE null mice

BACKGROUND

We previously showed that irradiation to the carotid arteries of ApoE(-/-) mice accelerated the development of macrophage-rich, inflammatory atherosclerotic lesions, prone to intra-plaque hemorrhage. In this study we investigated the potential of anti-inflammatory and anti-coagulant intervention strategies to inhibit age-related and radiation-induced atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

ApoE(-/-) mice were given 0 or 14 Gy to the neck and the carotid arteries and aortic arches were harvested at 4 or 30 weeks after irradiation. Nitric oxide releasing aspirin (NCX 4016, 60 mg/kg/day) or aspirin (ASA, 30 or 300 mg/kg/day) were given continuously in the chow. High dose ASA effectively blocked platelet aggregation, while the low dose ASA or NCX 4016 had no significant effect on platelet aggregation. High dose ASA, but not NCX 4016, inhibited endothelial cell expression of VCAM-1 and thrombomodulin in the carotid arteries at 4 weeks after irradiation; eNOS and ICAM-1 levels were unchanged. After 30 weeks of follow-up, NCX 4016 significantly reduced the total number of lesions and the number of initial macrophage-rich lesions in the carotid arteries of unirradiated mice, but these effects were not seen in the brachiocephalic artery of the aortic arch (BCA). In contrast, high dose ASA lead to a decrease in the number of initial lesions in the BCA, but not in the carotid artery. Both high dose ASA and NCX 4016 reduced the collagen content of advanced lesions and increased the total plaque burden in the BCA of unirradiated mice. At 30 weeks after irradiation, neither NCX 4016 nor ASA significantly influenced the number or distribution of lesions, but high dose ASA lead to formation of collagen-rich "stable" advanced lesions in carotid arteries. The total plaque area of the irradiated BCA was increased after ASA, but the plaque burden was very low compared with the carotid artery.

CONCLUSIONS/SIGNIFICANCE

The development and characteristics of radiation-induced atherosclerosis varied between different arteries but could not be circumvented by anti-inflammatory and anti-coagulant therapies. This implicates other underlying mechanistic pathways compared to age-related atherosclerosis.

Cyclic GMP signaling in cardiovascular pathophysiology and therapeutics

Cyclic guanosine 3',5'-monophosphate (cGMP) mediates a wide spectrum of physiologic processes in multiple cell types within the cardiovascular system. Dysfunctional signaling at any step of the cascade - cGMP synthesis, effector activation, or catabolism - have been implicated in numerous cardiovascular diseases, ranging from hypertension to atherosclerosis to cardiac hypertrophy and heart failure. In this review, we outline each step of the cGMP signaling cascade and discuss its regulation and physiologic effects within the cardiovascular system. In addition, we illustrate how cGMP signaling becomes dysregulated in specific cardiovascular disease states. The ubiquitous role cGMP plays in cardiac physiology and pathophysiology presents great opportunities for pharmacologic modulation of the cGMP signal in the treatment of cardiovascular diseases. We detail the various therapeutic interventional strategies that have been developed or are in development, summarizing relevant preclinical and clinical studies.

Nitric oxide: new evidence for novel therapeutic indications

BACKGROUND

Nitric oxide (NO) deficiency is implicated in many pathophysiological processes in mammals. NO is a ubiquitous molecule involved in multiple cellular functions. Uncontrolled or inappropriate production of NO may lead to several disease states including septic shock, rheumatoid and inflammatory arthropathies, and expansion of cerebral damage after stroke. However, to date, there are no therapeutic agents available that can overcome these conditions. Similarly, underproduction of NO by NO synthase or enhanced breakdown of NO also leads to diseases such as hypertension, ischemic conditions, pre-eclampsia, premature delivery, among others. NO donor therapies are indicated in these conditions.

RESULTS

Nitroglycerin and nitrates (NO donors) have been used as therapeutic agents for the past century, particularly to treat vascular disease, and the only significant adverse effects are headaches. NO donors are highly cost-effective and have beneficial effects in multiple body systems. When the body cannot generate NO via NO synthase or due to rapid turnover leading to inadequate amounts of NO available for biological homeostasis, administration of exogenous NO, or prolongation of the actions of endogenous NO, are practical ways to supplement NO.

CONCLUSION

Recipients of such therapy include patients with angina pectoris, coronary artery disease, hypertension, osteoporosis, gastrointestinal motility disorders, pregnancy-related disorders including premature delivery, pre-eclampsia, vulvodynia, and erectile dysfunction in men. Postmenopausal NO deficiency is rectified with hormone replacement therapy, which enhances local production of NO. Declining local NO production secondary to estrogen deficiency in postmenopausal women and perhaps in older men could be one of the reasons for age-related increased incidences of cardiovascular events and sexual dysfunction. Thus, in addition to supplementation of NO compounds in acute situations like alleviating angina and erectile dysfunction, chronic NO therapy is cost-effective in decreasing cardiovascular events, and improving the urogenital system and skeletal health.

Roles of platelet and endothelial cell COX-1 in hypercholesterolemia-induced microvascular dysfunction

Aspirin is a common preventative therapy in patients at risk for cardiovascular diseases, yet little is known about how aspirin protects the vasculature in hypercholesterolemia. The present study determines whether aspirin, nitric oxide-releasing aspirin (NCX-4016), a selective cyclooxygenase (COX)-1 inhibitor (SC560), or genetic deficiency of COX-1 prevents the inflammatory and prothrombogenic phenotype assumed by hypercholesterolemic (HC) venules. Aspirin or NCX-4016 (60 mg/kg) was administered orally for the last week of a 2-wk HC diet. COX-1-deficient (COX-1(-/-)) and wild-type (WT) mice were transplanted with WT (WT/COX-1(-/-)) or COX-1(-/-) (COX-1(-/-)/WT) bone marrow, respectively. HC-induced adhesion of platelets and leukocytes in murine intestinal venules, observed with intravital fluorescence microscopy, was greatly attenuated in aspirin-treated mice. Adhesion of aspirin-treated platelets in HC venules was comparable to untreated platelets, whereas adhesion of SC560-treated platelets was significantly attenuated. HC-induced leukocyte and platelet adhesion in COX-1(-/-)/WT chimeras was comparable to that in SC560-treated mice, whereas the largest reductions in blood cell adhesion were in WT/COX-1(-/-) chimeras. NCX-4016 treatment of platelet recipients or donors attenuated leukocyte and platelet adhesion independent of platelet COX-1 inhibition. Platelet- and endothelial cell-associated COX-1 promote microvascular inflammation and thrombogenesis during hypercholesterolemia, yet nitric oxide-releasing aspirin directly inhibits platelets independent of COX-1.

Building a better aspirin: gaseous solutions to a century-old problem

The gastrointestinal adverse effects of nonsteroidal anti-inflammatory drugs (NSAIDs) have been recognized since shortly after the introduction of aspirin to the marketplace over a century ago. However, the underlying pathogenesis of NSAID-induced gastropathy remains incompletely understood. Advances in understanding some of the factors that contribute to the mucosal injury have provided clues for the development of safer NSAIDs. The inhibitory effects of nitric oxide (NO) on NSAID-induced leukocyte adherence were exploited in the development of NO-releasing NSAIDs. As well as eliciting less gastrointestinal damage than conventional NSAIDs, these drugs do not elevate blood pressure and show anti-inflammatory effects, additional to those of the parent drugs. Modification of other drugs in a similar manner (i.e., NO-releasing derivatives) has similarly resulted in more effective drugs. More recently, hydrogen sulphide-releasing derivatives of NSAIDs and of other drugs, have been developed, based on the observed ability of H(2)S to reduce inflammation and pain in experimental models. H(2)S-releasing NSAIDs produce negligible gastric damage and exhibit enhanced anti-inflammatory potency as compared to the parent drugs. The NO-NSAIDs and H(2)S-releasing NSAIDs represent examples of new anti-inflammatory drugs with greatly reduced toxicity and improved therapeutic activity, both created through the concept of exploiting the beneficial effects of endogenous gaseous mediators.

NCX 6560, a nitric oxide-releasing derivative of atorvastatin, inhibits cholesterol biosynthesis and shows anti-inflammatory and anti-thrombotic properties

We compared the lipid-lowering, vasodilating, anti-thrombotic and anti-inflammatory properties of NCX 6560, a novel NO-releasing derivative of atorvastatin, with those of atorvastatin. NCX 6560 and atorvastatin induced similar inhibition of cholesterol biosynthesis in rat smooth muscle cells (IC(50)=1.9+/-0.4 and 3.9+/-1.0 microM, respectively). However, in hyperlipidemic mice, a 5-week oral treatment with NCX 6560 (46.8 mg/kg/day, p.o.) was more effective than equivalent atorvastatin (40 mg/kg/day, p.o.) at lowering serum cholesterol (NCX 6560: -21% vs controls, P<0.05; atorvastatin: -14% vs control, P=NS). In norepinephrine-precontracted rabbit aortic rings, NCX 6560-induced vasodilation (EC(50)=53.5+/-8.3 microM) and in PC12 cells it stimulated cGMP formation (EC(50)=1.8+/-0.7 microM), while atorvastatin was inactive. In lipopolysaccharide from Escherichia coli (LPS)-treated RAW 264.7 macrophages, NCX 6560 reduced iNOS expression and dimer assembly more efficiently than atorvastatin and inhibited nitrite accumulation (IC(50)=6.7+/-1.6 microM) and TNFalpha release. U46619- or collagen plus epinephrine-induced platelet pulmonary thromboembolism in mice was reduced by NCX 6560 at 46.8 mg/kg p.o. (mortality: -44% and -56% vs vehicle, respectively; P<0.05), but not by atorvastatin 40 mg/kg, p.o. In the U46619-induced mortality model, isosorbide mononitrate (ISMN) (20 mg/kg, p.o.), a pure NO-donor, was also active (mortality: -40%, P<0.05). NCX 6560 significantly reduced ex vivo platelet adhesion to collagen at high shear (-31+/-1.3% vs vehicle), and so did ISMN (-33.3+/-1.7% vs vehicle). Atorvastatin was ineffective. NCX 6560, but not atorvastatin, reduced blood pressure in eNOS knockout mice (-16%, P<0.001 vs vehicle), an effect not observed in wild type mice. On the contrary, ISMN provoked a significant drop of blood pressure both in wild type (-20%, P<0.05 vs vehicle) and in eNOS-/- mice (-21%, P<0.05 vs vehicle). In conclusion, NCX 6560 exerts greater lipid-lowering, anti-thrombotic and anti-inflammatory effects than atorvastatin, due to a large extent to NO release.

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.

Influence of nitric oxide-donating nonsteroidal anti-inflammatory drugs on the evolution of acute pancreatitis

Microcirculatory disturbances and leukocyte activation are main events in the pathogenesis of acute pancreatitis (AP) that is characterized by inflammatory up-regulation. Nitric oxide-donating nonsteroidal anti-inflammatory drugs (NO-NSAIDs) regulate vascular function and mitigate inflammation. To investigate the influence of NO-NSAIDs on AP. AP was induced by the biliopancreatic duct outlet exclusion-closed duodenal loops model. Treatment with NO-flurbiprofen, NO-ibuprofen, NO-aspirin, or their parental drugs was done (i) 1 h before, (ii) 1 h after, (iii) 1 h before and 4 h after, or (iv) 4 h after surgery. The degree of severity was evaluated using biochemical and histopathological analyses. NO-NSAIDs given before and during the first hour of the noxia decreased blood levels of amylase, lipase, C-reactive protein, IL-6, IL-10, heat shock protein 72, prostaglandin E2 inactive metabolite, and 8-isoprostane, as well as pancreatic and lung myeloperoxidase and cyclooxygenase. Acinar and fat necrosis, hemorrhage, and leukocyte infiltrate were also reduced. The best protection was achieved when treatment was performed 1 h before and 4 h after triggering AP. NO-flurbiprofen was the most effective drug. AP severity was significantly ameliorated by NO-NSAIDs being the administration time essential to achieve optimal pancreatic protection that may result to be useful in the prevention of postendoscopic severe AP.

Pharmacologic Profile and Therapeutic Potential of NCX 4016, a Nitric Oxide-releasing Aspirin, for Cardiovascular Disorders

NCX 4016, 2-(acetyloxy)benzoic acid 3-[(nitrooxy)methyl]phenyl ester, is a new molecule in which a nitric oxide (NO)-releasing moiety is covalently linked to aspirin. After enzymatic metabolism, NCX 4016 releases both components. In vitro and in some animal models, these components exert their pharmacologic effects simultaneously. Nitric oxide (NO) is a small gaseous molecule that exerts several activities which may prevent atherothrombotic disorders. Moreover, it displays a protective activity on the gastric mucosa. NCX 4016 has been shown to inhibit platelet activation in vitro more effectively than aspirin, to inhibit smooth muscle cell proliferation, to exert an endothelial cell protective activity and to suppress the function of several inflammatory cells potentially involved in atherothrombosis. In animal models, NCX 4016 protected from platelet thromboembolism, prevented restenosis in atherosclerosis-prone animals, protected the heart from ischemia/reperfusion injury, and induced neoangiogenesis in critically ischemic limbs. Moreover, it displayed little or no gastric toxicity and appeared to protect stomach from noxious stimuli, including aspirin. NCX 4016 has been evaluated in healthy volunteers and found to inhibit platelet cyclo-oxygenase-1 (COX-1) similarly to or slightly less than aspirin, to raise the circulating levels of NO-degradation products, and to have little or no gastric toxicity in short term studies. In particular, in phase II studies, NCX 4016 had favorable effects on effort-induced endothelial dysfunction in intermittent claudication and on platelet-activation parameters elicited by short-term hyperglycemia in type II diabetics. In patients with type II diabetes the effects of NCX 4016 on microalbuminuria and on some hemodynamic parameters were promising. The pharmacokinetics of in vivo aspirin- and NO- released by NCX 4016, as well as the bioavailability of the two molecules, were not yet adequately studied. Also, the long-term tolerability of NCX 4016, as well as its possible effectiveness in preventing ischemic cardiovascular events and progression of atherosclerosis, should be explored.

Influence of hydrocortisone, prednisolone, and NO association on the evolution of acute pancreatitis

Leukocyte activation, inflammatory up-regulation, and microcirculatory disruption associated with ischemia-reperfusion injury are hallmarks in the pathogenesis of acute pancreatitis (AP). NO donors ensure microvascular integrity, while glucocorticoids act as anti-inflammatory and immune modulator drugs. AP was induced by the biliopancreatic duct outlet exclusion-closed duodenal loops (BPDOE-CDLs) model. Treatment with hydrocortisone (6 mg/kg) or prednisolone (0.5 mg/kg) alone or together with DETA-NO (0.5 mg/kg) was done (a)1 hr pre or (b)1 hr post, or (c) 1 hr pre and 4 hr post ,or (d) 4 hr post triggering AP. NOS inhibition by L-NAME (15 mg/kg) and glucocorticoid receptor blockage by mifepristone (3 mg/kg) was considered. AP severity was assessed by biochemical and histopathological analyses. Treatment with glucocorticoids together with DETA-NO 1 hr pre and 4 hr post BPDOE-CDLs reduced serum amylase, lipase, C-reactive protein, IL-6, IL-10, hsp72, and 8-isoprostane as well as pancreatic and lung myeloperoxidase. Acinar and fat necrosis, hemorrhage, and neutrophil infiltrate were also decreased. Hydrocortisone together with DETA-NO rendered the best results. We conclude that AP severity was significantly diminished by glucocorticoids associated with DETA-NO, with the optimal dose and time point of administration being crucial to provide adequate protection against AP.

Cyclooxygenases, microsomal prostaglandin E synthase-1, and cardiovascular function

We investigated the mechanisms by which inhibitors of prostaglandin G/H synthase-2 (PGHS-2; known colloquially as COX-2) increase the incidence of myocardial infarction and stroke. These inhibitors are believed to exert both their beneficial and their adverse effects by suppression of PGHS-2-derived prostacyclin (PGI(2)) and PGE(2). Therefore, the challenge remains to identify a mechanism whereby PGI(2) and PGE(2) expression can be suppressed while avoiding adverse cardiovascular events. Here, selective inhibition, knockout, or mutation of PGHS-2, or deletion of the receptor for PGHS-2-derived PGI(2), was shown to accelerate thrombogenesis and elevate blood pressure in mice. These responses were attenuated by COX-1 knock down, which mimics the beneficial effects of low-dose aspirin. PGE(2) biosynthesis is catalyzed by the coordinate actions of COX enzymes and microsomal PGE synthase-1 (mPGES-1). We show that deletion of mPGES-1 depressed PGE(2) expression, augmented PGI(2) expression, and had no effect on thromboxane biosynthesis in vivo. Most importantly, mPGES-1 deletion affected neither thrombogenesis nor blood pressure. These results suggest that inhibitors of mPGES-1 may retain their antiinflammatory efficacy by depressing PGE(2), while avoiding the adverse cardiovascular consequences associated with PGHS-2-mediated PGI(2) suppression.

Molecular regulation of platelet-dependent thrombosis

Hemostasis is a normal process preventing the sequelae of uncontrolled hemorrhage. In certain settings, these same processes cause adverse clinical events due to thrombotic occlusion of a vessel. The majority of unstable coronary syndromes result from disruption of an atherosclerotic plaque, leading to the exposure of subintimal contents, which triggers coagulation and the formation of a platelet-rich thrombus. The central role of platelet activation in the events that lead to vessel occlusion is well known. However, this process is complex and influenced by a myriad of cellular and plasma-derived mediators that regulate the balance between occlusive and nonocclusive thrombosis.

Direct and irreversible inhibition of cyclooxygenase-1 by nitroaspirin (NCX 4016)

Benzoic acid, 2-(acetyl-oxy)-3-[(nitrooxy)methyl]phenyl ester (NCX 4016), a new drug made by an aspirin molecule linked, through a spacer, to a nitric oxide (NO)-donating moiety, is now under clinical testing for the treatment of atherothrombotic conditions. Aspirin exerts its antithrombotic activity by irreversibly inactivating platelet cyclooxygenase (COX)-1. NCX 4016 in vivo undergoes metabolism into deacetylated and/or denitrated metabolites, and it is not known whether NCX 4016 needs to liberate aspirin to inhibit COX-1, or whether it can block it as a whole molecule. The aim of our study was to evaluate the effects of NCX 4016 and its analog or metabolites on platelet COX-1 and whole blood COX-2 and on purified ovine COX (oCOX)-1 and oCOX-2. In particular, we have compared the mechanism by which NCX 4016 inhibits purified oCOX enzymes with that of aspirin using a spectrophotometric assay. All the NCX 4016 derivatives containing acetylsalicylic acid inhibited the activity of oCOX-1 and oCOX-2, whereas the deacetylated metabolites and the nitric oxide-donating moiety were inactive. Dialysis experiments showed that oCOX-1 inhibition by NCX 4016, similar to aspirin, is irreversible. Reversible COX inhibitors (indomethacin) or salicylic acid incubated with the enzyme before NCX 4016 prevent the irreversible inhibition of oCOX-1 by NCX 4016 as well as by aspirin. In conclusion, our data show that NCX 4016 acts as a direct and irreversible inhibitor of COX-1 and that the presence of a spacer and NO-donating moiety in the molecule slows the kinetics of COX-1 inhibition by NCX 4016, compared with aspirin.

A novel nitric oxide-releasing statin derivative exerts an antiplatelet/antithrombotic activity and inhibits tissue factor expression

BACKGROUND

NO-releasing statins are new chemical entities, combining HMG-CoA reductase inhibition and slow NO release, that possess stronger anti-inflammatory and antiproliferative activities than the native statins.

OBJECTIVE

We evaluated the antithrombotic effects of nitropravastatin (NCX-6550) by assessing its activity on platelet activation and tissue factor (TF) expression by mononuclear cells in vitro and in vivo.

METHODS AND RESULTS

In vitro, NCX-6550 inhibited (1) U46619- and collagen-induced platelet aggregation in buffer and plasma; (2) collagen-induced P-selectin expression in whole blood and (3) platelet adhesion to collagen-coated coverslips under high shear stress. These effects were displayed at concentrations of NCX-6550 ranging from 25 to 100 mum, and were totally reverted by the guanylylcyclase inhibitor ODQ (10 microm). Equimolar concentrations of pravastatin had no influence on these parameters of platelet function. LPS- and PMA-induced TF expression by blood mononuclear cells was also inhibited by NCX-6550 (IC50 13 microm), but not by pravastatin, as assessed by functional and immunological assays and by real-time PCR. In a mouse model of platelet pulmonary thromboembolism, induced by the i.v. injection of collagen plus epinephrine, pretreatment with NCX-6550 (24-48 mg kg(-1)) significantly reduced platelet consumption, lung vessel occlusion and mortality. Moreover, nitropravastatin markedly inhibited the generation of procoagulant activity by spleen mononuclear cells and peritoneal macrophages in mice treated with LPS. In these in vivo models too, pravastatin failed to affect platelet activation and monocyte/macrophage procoagulant activity.

CONCLUSIONS

Our results show that nitropravastatin exerts strong antithrombotic effects in vitro and in vivo, and may represent an interesting antiatherothrombotic agent for testing in acute coronary syndromes.

Endothelial cell dysfunction: can't live with it, how to live without it

Endothelial cell dysfunction is emerging as an ultimate culprit for diverse cardiovascular diseases and cardiovascular complications of chronic renal diseases, yet the definition of this new syndrome, its pathophysiology, and therapy remain poorly defined. Here, I summarize some molecular mechanisms leading from hyperhomocystinemia, elevated asymmetric dimethylarginine, and advanced glycolation end product-modified protein level to the proatherogenic, prothrombogenic, and proinflammatory endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions. Finally, several therapeutic strategies to prevent and correct endothelial dysfunction are discussed in the light of uncertainty of their action modulated by the endothelial dysfunction per se.

Co-administration of nitric oxide-aspirin (NCX-4016) and aspirin prevents platelet and monocyte activation and protects against gastric damage induced by aspirin in humans

OBJECTIVES

The goal of this study was to test the hypothesis that NCX-4016 may have broader anti-inflammatory and antithrombotic effects as well as better gastric tolerability than aspirin in humans.

BACKGROUND

NCX-4016 is an aspirin derivative containing a nitric oxide-releasing moiety that prevents platelet activation and modulates tissue factor (TF) expression and cytokine release from lipopolysaccharide (LPS)-stimulated monocytes.

METHODS

This was a blind-observer, placebo-controlled, parallel-group study in which 48 healthy subjects were randomized to receive NCX-4016 800 mg twice a day, NCX-4016 800 mg twice a day plus aspirin 325 mg, aspirin 325 mg, or placebo for 21 days.

RESULTS

Similar to aspirin alone, NCX-4016 effectively inhibited platelet aggregation induced by 0.6 mmol/ arachidonic acid, clot-stimulated thromboxane (TX) B2 generation in whole blood, and urinary excretion of 11-dehydro-TXB2. Unlike aspirin alone, the administration of NCX-4016 significantly inhibited TF expression in monocytes stimulated ex vivo with 10 micromol/l LPS (determined by flow-cytometry analysis of TF on CD14 positive cells). NCX-4016 also inhibited the rapid TF expression induced in monocytes by a proteinase activated receptor agonist (thrombin receptor activator protein, 2 micromol/l) as well as LPS-induced expression of CD11b . Ex vivo, release of MCP-1 and interleukin-6 were significantly inhibited by NCX-4016, but not by aspirin. NCX-4016 was not associated with gastric damage, and significantly reduced gastric injury when co-administered with aspirin, although both drugs reduced gastric PGE2 production to the same extent.

CONCLUSIONS

NCX-4016 is equally effective as aspirin in inhibiting cyclooxygenase activity. However, NCX-4016 causes less gastric damage and prevents monocyte activation. Larger multicenter trials are warranted to establish clinical efficacy and safety of NCX-4016.

Nitric oxide-releasing aspirin derivative, NCX 4016, promotes reparative angiogenesis and prevents apoptosis and oxidative stress in a mouse model of peripheral ischemia

BACKGROUND

Recently, nitric oxide (NO) donors have been developed that mimic the physiological intracellular release of NO. We evaluated whether one of these new compounds, consisting of aspirin coupled to an NO-releasing moiety (NCX 4016), would protect limbs from supervening arterial occlusion.

METHODS AND RESULTS

Mice were assigned to receive regular chow or chow containing NCX 4016 or aspirin (both at 300 mumol/kg body weight, daily) throughout the 3-week experimental period. One week after randomization, they underwent surgical excision of the left femoral artery. Limb blood flow recovery (laser Doppler flowmetry) was accelerated by NCX 4016 as compared with aspirin or vehicle (P<0.05). In controls, histological analysis revealed a 35% increase in the capillary density of ischemic muscles compared with contralateral ones, indicative of spontaneous angiogenesis. Neovascularization was enhanced by NCX 4016 (91%; P<0.05 versus vehicle), but not by aspirin (51%; P=NS versus vehicle). Furthermore, NCX 4016 reduced endothelial cell (EC) apoptosis (4.3+/-1.0 versus 8.7+/-2.0 in aspirin and 12.6+/-3.3 ECs/1000 cap in vehicle; P<0.05 for either comparison) as well as caspase-3 mRNA levels in ischemic muscles ([caspase-3/GAPDH]*100 = 0.09+/-0.04 versus 2.30+/-0.44 in aspirin and 2.30+/-0.32 in vehicle; P<0.01 for either comparison). Nitrite levels and the ratio of reduced to oxidized glutathione were selectively increased in ischemic muscles by NCX 4016. Vascular endothelial growth factor-A expression was reduced by aspirin, with this effect being blunted by NCX 4016.

CONCLUSIONS

Pretreatment with the new oral NO-releasing aspirin derivative stimulates reparative angiogenesis and prevents apoptosis and oxidative stress, thereby alleviating the consequences of supervening arterial occlusion.

Gastric tolerability and prolonged prostaglandin inhibition in the brain with a nitric oxide-releasing flurbiprofen derivative, NCX-2216 [3-[4-(2-fluoro-alpha-methyl-[1,1'-biphenyl]-4-acetyloxy)-3-methoxyphenyl]-2-propenoic acid 4-nitrooxy butyl ester]

NCX-2216 [3-[4-(2-fluoro-alpha-methyl-[1,1'-biphenyl]-4-acetyloxy)-3-methoxyphenyl]-2-propenoic acid 4-nitrooxy butyl ester] is an NO-releasing flurbiprofen derivative that also contains a ferulic acid (antioxidant) moiety. NCX-2216 has been shown to be effective in reducing beta-amyloid deposition in a transgenic mouse model of Alzheimer's disease. The tolerability of this compound in the stomach and its ability to suppress prostaglandin synthesis in the brain are not known. The purpose of this study was to assess the contribution of nitric oxide (NO) and ferulic acid to the pharmacological properties of NCX-2216 versus flurbiprofen; thus, we compared their gastric tolerability and suppression of prostaglandin synthesis, peripherally and centrally. Oral flurbiprofen produced extensive gastric damage and suppressed gastric prostaglandin synthesis. In contrast, while suppressing prostaglandin production, equimolar doses of NCX-2216 did not cause detectable gastric injury. The NO-releasing moiety of NCX-2216 (but not the ferulic acid moiety) was crucial for the gastric safety of this compound. NCX-2216 substantially inhibited prostanoid synthesis despite not being detectable in plasma and despite producing only low amounts of flurbiprofen in plasma and in the brain. Inhibition of brain prostaglandin synthesis by NCX-2216 (22 mg/kg) persisted for a much longer period of time (up to 48 h) than was seen with flurbiprofen ( Collapse

Key Words Collapse

MESH Headings

• Animals
• Antioxidants/pharmacology
• Brain/drug effects
• Brain/metabolism
• Cyclooxygenase Inhibitors/pharmacokinetics
• Cyclooxygenase Inhibitors/pharmacology
• Flurbiprofen/analogs & derivatives
• Flurbiprofen/blood
• Flurbiprofen/cerebrospinal fluid
• Flurbiprofen/pharmacokinetics
• Flurbiprofen/pharmacology
• Male
• Mice
• Nitric Oxide/metabolism
• Prostaglandin Antagonists/blood
• Prostaglandin Antagonists/cerebrospinal fluid
• Prostaglandin Antagonists/pharmacology
• Prostaglandin-Endoperoxide Synthases/metabolism
• Prostaglandins/metabolism
• Rats
• Rats, Wistar
• Stomach/drug effects

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Grants Collapse

Affiliation(s)

John L Wallace Department of Pharmacology and Therapeutics, University of Calgary, Alberta, Canada.
Marcelo N Muscará
Gilberto de Nucci
Stella Zamuner
Giuseppe Cirino
Piero del Soldato
Ennio Ongini

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Platelets, atherosclerosis and the endothelium: new therapeutic targets?

One of the major causes of morbidity and mortality in the developed world is atherosclerosis. Recent research has suggested that the interaction of platelets with the endothelium is important in both the progression of atherosclerosis and the development of the acute complications of the disease. Both of these cells secrete various signalling molecules and express adhesion molecules, which can influence the development of pathological states. Certainly, there may be a vicious cycle in which platelet activation promotes atherosclerosis; a process involving inflammation and the activation of many other cell types (for example, leukocytes and smooth muscle cells), which causes further platelet activation. Therefore, intense effort has been made to develop therapeutic agents that can modulate the function of these cells, with the ultimate aim to retard (or even reverse) the progression of atheroma growth.

Antioxidant activity of nitro derivative of aspirin against ischemia-reperfusion in hamster cheek pouch microcirculation

Aspirin that has been chemically combined with a nitric oxide (NO) donor (NCX-4016) has been shown to inhibit cyclooxygenase and prostaglandin generation while maintaining the inhibitory effects of aspirin. The possible role of reactive oxygen species (ROS) in the action of NCX-4016 in ischemia-reperfusion (I/R) has not been studied. Furthermore, we were interested in comparing the effects of a conventional NO donor [2,2'-hydroxynitrosohydrazino-bis-etanamine (DETA/NO)] and NCX-4016 at the microvascular level in the hamster cheek pouch visualized by using an intravital fluorescent microscopy technique. Microvascular injury was assessed by measuring diameter change, the perfused capillary length (PCL), and leukocyte adhesion. Animals were treated with NCX-4016 (100 mg/kg or 30 mg.kg(-1).day(-1) for 5 days po) or DETA-NO (0.5 mg/kg). Mean arterial blood pressure increased slightly but significantly after NCX-4016 treatment. During 5- and 15-min reperfusion, lipid peroxides in the systemic blood increased by 72 and 89% vs. baseline, respectively, and were still higher than in basal conditions after 30-min reperfusion in the I/R group. Pretreatment with NCX-4016 maintained ROS at normal levels; increased arteriolar diameter, blood flow, and PCL; and decreased leukocyte adhesion (P < 0.05). DETA-NO decreased ROS during 30-min reperfusion; however, later there was a significant increase during reperfusion. DETA-NO decreased leukocyte adhesion (P < 0.05) but microvascular permeability increased after 30 min of reperfusion. In conclusion, NCX-4016 attenuates oxidative stress and prevents arteriolar constriction during I/R, whereas DETA-NO increases lipid peroxides in the systemic blood and permeability after reperfusion.

Effects of subacute treatment with benzopyranopyrimidines in hemostasis and experimental thrombosis in mice

The antithrombotic activity of a series of benzopyranopyrimidine derivatives was investigated in platelet-dependent and independent pulmonary thromboembolism in mice. Intraperitoneal subacute treatment with 2-morpholino derivative 3c significantly prevented paralysis due to collagen plus epinephrine-induced pulmonary thrombosis while 2-piperidino substituted derivative 3h significantly protected mice from paralysis caused by thrombin-induced intravascular fibrin formation at dosage not affecting bleeding time. These compounds, previously proved to be effective as antiplatelet agents in vitro, were in vivo more potent as antithrombotics than lysine acetylsalicylate and possessed lower prohemorrhagic activity than the reference drug. Although their ineffectiveness on clotting times, PT and APTT, allows the involvement of coagulation pathways to be ruled out, the mechanisms underlying the favourable benefit risk ratio for these two compounds remain to be further clarified.

Antinociception and the new COX inhibitors: research approaches and clinical perspectives

New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their traditional parent compounds. They are also safer than the classic non-steroidal anti-inflammatory drugs (NSAIDs) and are starting to be used not only for low to moderate intensity pain, but also for high intensity pain. Three different strategies have been followed to improve the pharmacological profile of COX inhibitors: 1. Development of COX-2 selective inhibitors. This is based on the initial hypothesis that considered COX-2 as the enzyme responsible for the generation of prostaglandins only in inflammation, and, therefore, uniquely responsible for inflammation, pain and fever. Initial expectations gave rise to controversial results, still under discussion. The second generation of these compounds is being developed and should contribute to clarifying both their efficacy and the specific functions of the COX enzymes. 2. Modified non-selective COX inhibitors. Molecules like nitro-NSAIDs or tromethamine salt derivatives have been synthesized considering that both COX-1 and COX-2 are responsible for the synthesis of prostaglandins involved either in homeostatic functions or inflammation. Nitroaspirin, nitroparacetamol or dexketoprofen trometamol are some examples of molecules that are already showing an important clinical efficacy. The modifications performed in their structures seem to lower the unwanted side effects as well as to enhance their analgesic efficacy. 3. Combined therapy of classic NSAIDs with other drugs. This strategy looks for improvements in the incidence of adverse effects or to take advantage of the synergistic enhancement of their therapeutic effects. Some of the molecules resulting from these strategies are very valuable as therapeutic agents and open a wide range of possibilities in the treatment of high intensity pain, including neuropathic pain, and opiate sparing therapy.

Nitric oxide-releasing drugs

Pharmacological compounds that release nitric oxide (NO) have been useful tools for evaluating the broad role of NO in physiology and therapeutics. NO deficiency has been implicated in the genesis and evolution of several disease states. Both medical needs and commercial opportunities have fostered attempts to modulate NO in the human body for therapeutic gain. Strategies for NO modulation encompass antiinflammatory, sexual dysfunction, and cardiovascular indications. Apart from newly developed drugs, several commonly used cardiovascular drugs exert their beneficial action, at least in part, by modulating the NO pathway. This review discusses the fundamental pharmacological properties and mechanisms of action of NO-releasing drugs. Some of these compounds may enter in the clinical arena providing important therapeutic benefits in human diseases.

Alpha2-antiplasmin plays a significant role in acute pulmonary embolism

The importance of pulmonary embolism (PE) due to venous thrombosis is recognized in the treatment of vascular diseases. We have investigated the physiological effects of plasmin generation in experimental acute PE using mice deficient in plasminogen (Plg-/-) or alpha2-antiplasmin (alpha2-AP-/-). PE was induced by continuous induction of venous thrombus in the left jugular vein by endothelial injury due to photochemical reaction. The mortality of wild-type mice was 68.8% at 2 h after the initiation of venous thrombosis and it was significantly reduced in alpha2-AP-/- mice (41.7%). In contrast, Plg-/- mice did not survive. Histological evidence of thromboembolism in the lung was obtained in all mice. However, whereas a strict thromboembolism was observed in Plg-/- mice, only a few thrombi were detected in the lungs of alpha2-AP-/- mice. Plasma fibrinogen levels measured in mice were not different. When alpha2-AP was infused in alpha2-AP-/- mice, the mortality was indistinguishable from wild-type mice. Tissue-type plasminogen activator (tPA) did not reduce the mortality due to acute PE in wild-type mice. However, in alpha2-AP-/- mice, tPA (0.52 mg x kg-1) significantly decreased the mortality compared with that of alpha2-AP-/- mice without tPA. The bleeding time was not significantly prolonged in either type of mice treated with tPA. The lack of plasminogen increases the mortality due to acute PE while a lack of alpha2-AP decreases the mortality rate, which can be further reduced by tPA administration. Therefore, the combination of inhibition of alpha2-AP with thrombolytic therapy could be beneficial in the treatment of acute PE.

NO-aspirin: mechanism of action and gastrointestinal safety

Nitric oxide-releasing aspirins are new chemical entities obtained by adding a nitric oxide-releasing moiety to aspirin. NCX-4016 is the prototype of this family of molecules. NCX-4016 consists of the parent molecule (aspirin) linked to a 'spacer' via an ester linkage, which is in turn connected to a nitric oxide-releasing moiety. Both aspirin and nitric oxide moieties of NCX-4016 contribute to its effectiveness, the latter occurring via both cyclic guanosyl monophosphate-dependent and -independent mechanisms. In vitro studies have shown that NCX-4016 inhibits platelet aggregation induced by aspirin-sensitive (arachidonic acid) and aspirin-insensitive (thrombin) agonist. In contrast to aspirin, NCX-4016 exerts a multilevel regulation of inflammatory target, including caspase-1 and NF-kappaB. This broad spectrum of activities translates to an increased potency of this drug in modulating cardiovascular inflammation. Human studies have shown, that while nitric oxide-aspirin maintains its anti-thrombotic activity, it spares the gastrointestinal tract. Indeed, a 7-day course of NCX-4016 results in 90% reduction of gastric damage caused by equimolar doses of aspirin. Further studies are ongoing to define whether this superior anti-inflammatory and anti-thrombotic profile translates in clinical benefits in patients with cardiovascular diseases.

New antithrombotic drugs on the horizon

Venous and arterial thromboembolism are a major cause for morbidity and mortality. The list of established drugs for the prevention of thrombus formation and embolisation includes heparins, hirudin and derivatives, aspirin, ADP and glycoprotein IIb/IIIa receptor antagonists, as well as vitamin K antagonists. Several limitations exist for these drugs that have stimulated the search for new and better anticoagulants. A series of selective clotting factor Xa inhibitors and direct factor IIa (thrombin) inhibitors are on the horizon, two of which are getting close to broad clinical application. Additional therapeutics that are still under preclinical and clinical investigation include inhibitors of the tissue factor pathway/factor VII complex, clotting factor VIII and XIII inhibitors and modulators of the protein C pathway or of endogenous fibrinolysis, as well as novel antiplatelet drugs. This review is focused on the current status of development of novel antithrombotics and their clinical potential. Even though only a few of a broad array of antithrombotic agents have reached clinical testing, some hold the potential for significant improvement in efficacy and safety of anticoagulant therapy.

NCX4016: a novel antithrombotic agent

Despite great advantages in antithrombotic treatments, important limitations of the presently available drugs encourage the search of more effective agents. Within the cardiovascular system, nitric oxide exerts several activities which may have an antithrombotic potential. Nitroaspirin in vitro inhibits platelet aggregation and adhesion under shear conditions and smooth muscle cell proliferation--all activities not exerted by aspirin. In vivo nitroaspirin exerts antithrombotic properties and prevents restenosis in hypercholesterolemic mice while aspirin is inactive. Nitroaspirin has shown a number of significant advantages over the presently available antiplatelet agents; however, only clinical studies will say whether nitroaspirin represents a step forward in antithrombotic treatment.

Gastrointestinal safety of NO-aspirin (NCX-4016) in healthy human volunteers: a proof of concept endoscopic study

BACKGROUND AND AIMS

NCX-4016 is a nitric oxide-releasing derivative of aspirin with antiplatelet activity. The aim of this study was to investigate the effect of NCX-4016 on gastrointestinal mucosa and platelet functions in healthy human volunteers.

METHODS

This was a parallel-group, double-blind, placebo-controlled study. Forty healthy subjects were randomly allocated to receive 7 days of treatment with NCX-4016 (400 and 800 mg twice daily), equimolar doses of aspirin (200 and 420 mg twice daily), or placebo. Upper endoscopies were performed before and at the end of the treatment period, and gastroduodenal lesions were graded using a predefined scoring system. Basal and posttreatment platelet aggregation in response to arachidonic acid (AA) and serum thromboxane (TX) B(2) and AA-stimulated platelet TXB(2) production were investigated.

RESULTS

Mucosal endoscopic injury score on day 7 was 0.63 +/- 0.16 in the placebo group and 11.0 +/- 3.0 and 16.1 +/- 1.6 in healthy volunteers treated with 200 and 420 mg aspirin twice daily (P < 0.0001 vs. placebo). NCX-4016 was virtually devoid of gastric and duodenal toxicity, resulting in a total gastric and duodenal endoscopic score of 1.38 +/- 0.3 and 1.25 +/- 0.5 (P < 0.0001 vs. aspirin, not significant vs. placebo). NCX-4016 inhibited AA-induced platelet aggregation as well as serum TXB(2) and platelet TXB(2) generation induced by AA to the same extent as aspirin (not significant vs. aspirin).

CONCLUSIONS

In this study, we have proven the concept that addition of an NO-donating moiety to aspirin results in a new chemical entity that maintains cyclooxygenase-1 and platelet inhibitory activity while nearly avoiding gastrointestinal damage.

The therapeutic potential of NO-NSAIDs

NSAIDs, including those that are selective for cyclooxygenase-2, are among the most widely used drugs. However, these drugs produce significant side effects in the gastrointestinal and cardiorenal systems, which greatly limit their utility. In recent years, a new type of anti-inflammatory agent has been developed that appears to offer significant advantages over conventional and Cox-2-selective NSAIDs. No-NSAIDs are derivatives of conventional NSAIDs, which are able to release nitric oxide over prolonged periods of time. The combination of balanced inhibition of the two main isoforms of COX with controlled release of nitric oxide yields a series of drugs that exert anti-inflammatory and analgesic activities in a wide range of settings, and have markedly reduced gastrointestinal and cardiorenal toxicity. Recent clinical trials of NO-NSAIDs have provided a 'proof of concept' that is completely consistent with pre-clinical characterization of these compounds.

NCX-4016 (NO-aspirin) inhibits lipopolysaccharide-induced tissue factor expression in vivo: role of nitric oxide

BACKGROUND

NCX-4016 is an acetylsalicylic acid (ASA) derivative containing a nitric oxide-releasing moiety. Compared with ASA, NCX-4016 has a broader spectrum of antithrombotic and antiinflammatory activities. We hypothesized that NCX-4016 might inhibit in vivo lipopolysaccharide (LPS)-induced expression of tissue factor (TF).

METHODS AND RESULTS

Rats were administered 90 mg/kg NCX-4016 orally for 5 days. Placebo, 50 mg/kg ASA, and 80 mg/kg isosorbide-5-mononitrate (ISMN) were used in control groups. On day 5, rats were injected intraperitoneally with 100 microg/kg LPS and killed 6 hours later. The expression of TF in monocytes was measured by flow cytometry and Western blot analysis. Reverse transcriptase-polymerase chain reaction was performed to assess expression of TF and cyclooxygenase-2 (COX-2) genes. Plasma concentrations of interleukin-1beta and tumor necrosis factor-alpha were measured. Urine samples were collected to evaluate the excretion of the thromboxane metabolite 11-dehydro-thromboxane (TX)B2. Gastric mucosa was inspected. LPS injection was followed by synthesis TF and COX-2 mRNAs in circulating monocytes, which were blunted by NCX-4016 but not by ASA or ISMN. Both NCX-4016 and ISMN reduced TF expression on surface of circulating monocyte. LPS increased the excretion 11-dehydro-TXB2, and this was prevented by NCX-4016 and ASA. Unlike ASA, NCX-4016 reduced plasma interleukin-1beta and tumor necrosis factor-alpha. In addition, NCX-4016 almost completely prevented mucosal damage, whereas ASA increased the extension of gastric lesions in LPS-injected rats.

CONCLUSIONS

NCX-4016 prevents monocyte TF expression; this is accompanied by inhibition of TX and cytokine biosynthesis. These additive effects of nitric oxide release and COX inhibition may help explain efficacy and tolerability of NCX-4016.

Pharmacology and potential therapeutic applications of nitric oxide-releasing non-steroidal anti-inflammatory and related nitric oxide-donating drugs

This review examines the biological significance, therapeutic potential and mechanism(s) of action of a range of nitric oxide-releasing non-steroidal anti-inflammatory drugs (NO-NSAID) and related nitric oxide-releasing donating drugs (NODD). The slow release of nitric oxide (NO) from these compounds leads to subtle changes in the profile of pharmacological activity of the parent, non-steroidal anti-inflammatory drugs (NSAID). For example, compared with NSAID, NO-NSAID cause markedly diminished gastrointestinal toxicity and improved anti-inflammatory and anti-nociceptive efficacy. In addition, nitroparacetamol exhibits hepatoprotection as opposed to the hepatotoxic activity of paracetamol. The possibility that NO-NSAID or NODD may be of therapeutic benefit in a wide variety of disease states including pain and inflammation, thrombosis and restenosis, neurodegenerative diseases of the central nervous system, colitis, cancer, urinary incontinence, liver disease, impotence, bronchial asthma and osteoporosis is discussed.

Nitric oxide donor drugs: current status and future trends

Nitric oxide synthesised in endothelial cells that line blood vessels has a wide range of functions that are vital for maintaining a healthy cardiovascular system. Reduced nitric oxide availability is implicated in the initiation and progression of many cardiovascular diseases and delivery of supplementary nitric oxide to help prevent disease progression is an attractive therapeutic option. Nitric oxide donor drugs represent a useful means of systemic nitric oxide delivery and organic nitrates have been used for many years as effective therapies for symptomatic relief from angina. However, nitrates have limitations and a number of alternative nitric oxide donor classes have emerged since the discovery that nitric oxide is a crucial biological mediator. This review focuses on novel advances and possible future directions in nitric oxide donor drug development.

Nitric oxide-releasing drugs: a novel class of effective and safe therapeutic agents

Nitric oxide (NO) deficiency has been implicated in many pathologic processes, thus providing a solid biological basis for the use of NO replacement therapy. Exogenous NO sources constitute a powerful way to supplement NO when the body cannot generate sufficient NO for normal biological functions. This theory has opened up the possibility of designing new drugs that are capable of delivering NO into tissues and the bloodstream in a sustained and controlled manner. This objective has been achieved by grafting an organic nitrate structure onto existing drugs through chemical spacers, such as aliphatic, aromatic, or a heterocyclic chain. The approach has led to the synthesis of several new chemical entities whose pharmacologic profile challenges the parent drug, not only on the basis of new properties, but also with respect to a better safety profile. In this article, a specific class of NO donors is reviewed, the nitric oxide-releasing non-steroidal antiinflammatory drugs, NO-NSAIDs. Recently discovered compounds, whose action depends on the combined properties of both the known drug and NO release, are illustrated. Two examples are described in detail: (1) nitric oxide-releasing aspirin, which has demonstrable innovative properties for treatment of vascular disorders and cancer; (2) nitro-derivatives of flurbiprofen that have shown encouraging results in models of Alzheimer's disease.

Potential cardioprotective actions of no-releasing aspirin

The use of low doses of aspirin on a daily basis has increased greatly in the past 20 years, based on observations that it can significantly reduce the risk of heart attacks and strokes. However, aspirin can also cause severe damage to the stomach. A modified version of aspirin that releases nitric oxide has been developed that seems to offer important advantages over its 103-year-old parent--namely, improved protection for the heart without the unwanted effects on the stomach.

Platelets inhibit the lysis of pulmonary microemboli

Using tracings of (125)I-labeled fibrin(ogen) in rodents, we examined the hypothesis that platelets impede the lysis of pulmonary emboli. (125)I-Microemboli (ME, 3-10 micron diameter) lodged homogeneously throughout the lungs after intravenous injection in both rats and mice (60% of injected dose), caused no lethality, and underwent spontaneous dissolution (50 and 100% within 1 and 5 h, respectively). Although lung homogenates displayed the most intense fibrinolytic activity of all the major organs, dissolution of ME was much slower in isolated perfused lungs (IPL) than was observed in vivo. Addition of rat plasma to the perfusate facilitated ME dissolution in IPL to a greater extent than did addition of tissue-type plasminogen activator alone, suggesting that permeation of the clot by plasminogen is the rate-limited step in lysis. Platelet-containing ME injected in rats lysed much more slowly than did ME formed from fibrin alone. (125)I-Thrombi, formed in the pulmonary vasculature of mice in response to intravascular activation of platelets by injection of collagen and epinephrine, were essentially resistant to spontaneous dissolution. Moreover, injection of the antiplatelet glycoprotein IIb/IIIa antibody 7E3 F(ab')(2) facilitated spontaneous dissolution of pulmonary ME and augmented fibrinolysis by a marginally effective dose of Retavase (10 microg/kg) in rats. These studies show that platelets suppress pulmonary fibrinolysis. The mechanism(s) by which platelets stabilize ME and utility of platelet inhibitors to facilitate their dissolution deserves further study.

Colon cancer prevention with NO-releasing NSAIDs

A seminal advance in the prevention of colon cancer has been the observation that nonsteroidal antiinflammatory drugs (NSAIDs) reduce the incidence of and mortality from colon cancer by about half. Among current efforts to overcome the side effects of NSAIDs, an important limitation for their application as chemopreventive agents, is the synthesis of nitric oxide-releasing NSAIDs. These novel compounds may display greater safety and greater efficacy compared to their parent traditional NSAIDs and thus hold significant promise as chemopreventive agents against human colon cancer. In this review we discuss salient features of their pharmacology, in vitro and animal data pertaining to colon cancer, their mechanisms of action, and assess their potential in the chemoprevention of colon cancer.

Nitric oxide donors and cardiovascular agents modulating the bioactivity of nitric oxide: an overview

Nitric oxide (NO) mediates multiple physiological and pathophysiological processes in the cardiovascular system. Pharmacological compounds that release NO have been useful tools for evaluating the pivotal role of NO in cardiovascular physiology and therapeutics. These agents constitute two broad classes of compounds, those that release NO or one of its redox congeners spontaneously and those that require enzymatic metabolism to generate NO. In addition, several commonly used cardiovascular drugs exert their beneficial action, in part, by modulating the NO pathway. Here, we review these classes of agents, summarizing their fundamental chemistry and pharmacology, and provide an overview of their cardiovascular mechanisms of action.