cyclic-gmp and Thromboembolism

Nitric oxide (NO) activates soluble guanylate cyclase (sGC) by binding its prosthetic heme group, thereby catalyzing cyclic guanosine monophosphate (cGMP) synthesis. cGMP causes vasodilation and may inhibit smooth muscle cell proliferation and platelet aggregation. The NO-sGC-cGMP pathway is disordered in pulmonary arterial hypertension (PAH), a syndrome in which pulmonary vascular obstruction, inflammation, thrombosis, and constriction ultimately lead to death from right heart failure. Expression of sGC is increased in PAH but its function is reduced by decreased NO bioavailability, sGC oxidation and the related loss of sGC's heme group. Two classes of sGC modulators offer promise in PAH. sGC stimulators (e.g., riociguat) require heme-containing sGC to catalyze cGMP production, whereas sGC activators (e.g., cinaciguat) activate heme-free sGC. Riociguat is approved for PAH and yields functional and hemodynamic benefits similar to other therapies. Its main serious adverse effect is dose-dependent hypotension. Riociguat is also approved for inoperable chronic thromboembolic pulmonary hypertension.

Topics: Animals; Benzoates; Chronic Disease; Cyclic GMP; Drug Design; Guanylate Cyclase; Humans; Hypertension, Pulmonary; Nitric Oxide; Pyrazoles; Pyrimidines; Receptors, Cytoplasmic and Nuclear; Soluble Guanylyl Cyclase; Thromboembolism

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia, which confers a high risk of mortality and morbidity from stroke and thromboembolism. The precise mechanisms by which AF causes thromboembolism and subsequent cerebrovascular events have attracted much research interest, and are yet to be fully elucidated. Nonetheless, it is well recognised that AF fulfils Virchow's triad for thrombogenesis, with abnormal flow conditions with loss of atrial contractility and an irregularly irregular cardiac output, (i. e. flow abnormalities), as well as structural heart disease with endocardial damage (i. e. abnormal vessel wall) and abnormalities in platelet and haemostatic variables (i. e. abnormal blood constituents). This review is to summarise the evidence so far for the role of coagulation and fibrinolytic components, platelets and inflammation (that is blood constituents) in the generation of the prothrombotic state in AF, with particular focus on the endothelium and AF.

Topics: Atrial Fibrillation; Cyclic GMP; Endothelium, Vascular; Fibrinolysis; Hemostasis; Humans; Nitric Oxide; Stroke; Thromboembolism; Thromboplastin; von Willebrand Factor

When pulmonary hypertension results in marked limitation in activities of daily living (functional class III), the first-choice vasodilator is bosentan, despite its limitations. There is no proven advantage of adding another vasodilator. The adverse effects of vasodilators outweigh their uncertain efficacy in patients with only a slight limitation of physical activity (class II). When surgery is not feasible or when chronic thromboembolic pulmonary hypertension persists despite surgery, there are no vasodilators with a favourable harm-benefit balance. Riociguat (Adempas, Bayer) is a vasodilator that acts by enhancing the synthesis of cyclic guanosine monophosphate (cGMP), a mediator of vasodilation. This mechanism of action is similar to that of sildenafil, which inhibits cGMP catabolism. Riociguat has been authorised in the European Union in adult patients with class II or III pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension. Riociguat monotherapy has not been compared with another vasodilator in patients with pulmonary arterial hypertension. In a 12-week randomised, double-blind, placebo-controlled trial in 380 patients, riociguat had modest symptomatic efficacy, improving the functional class in 21% of patients (versus 14% in the placebo arm). There was no statistically significant difference in mortality. The symptomatic benefit appeared to be similar in patients who continued to take bosentan and in those who were not taking a vasodilator other than riociguat. In a 16-week, double-blind trial in 261 patients with chronic thromboembolic pulmonary hypertension in whom surgery was not feasible or had failed, riociguat was more effective than placebo on symptoms; there was improvement in functional class in respectively 33% and 15% of patients. There was no statistically significant change in mortality. In these two clinical situations, subgroup analyses showed no benefit of riociguat in patients who had only slight limitation of physical activity (class II). The main adverse effects of riociguat are related to its vasodilatory properties, and include headache, arterial hypotension, dizziness and peripheral oedema. Riociguat can also cause bleeding, including potentially severe pulmonary haemorrhage. More data are needed on its cardiac, renal and osseous adverse effects. Riociguat is subject to pharmacodynamic interactions with many other drugs. In particular, riociguat coadministration with a phosphodiesterase type 5 inhi

Topics: Activities of Daily Living; Adult; Animals; Chronic Disease; Cyclic GMP; Humans; Hypertension, Pulmonary; Motor Activity; Pyrazoles; Pyrimidines; Thromboembolism; Vasodilator Agents

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.. 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.. 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.

Topics: Adrenergic beta-1 Receptor Antagonists; Animals; Antioxidants; Benzopyrans; Blood Platelets; Blood Pressure; Cyclic GMP; Disease Models, Animal; Dose-Response Relationship, Drug; Ethanolamines; Fibrinolytic Agents; Isomerism; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nebivolol; Nitric Oxide; Nitric Oxide Synthase Type III; Phosphorylation; Platelet Activation; Platelet Aggregation Inhibitors; Selenoprotein P; Thromboembolism; Thrombosis; Time Factors; Up-Regulation

Amarogentin, an active principle of Gentiana lutea, possess antitumorigenic, antidiabetic, and antioxidative properties. Activation of platelets is associated with intravascular thrombosis and cardiovascular diseases. The present study examined the effects of amarogentin on platelet activation. Amarogentin treatment (15~60  μM) inhibited platelet aggregation induced by collagen, but not thrombin, arachidonic acid, and U46619. Amarogentin inhibited collagen-induced phosphorylation of phospholipase C (PLC) γ2, protein kinase C (PKC), and mitogen-activated protein kinases (MAPKs). It also inhibits in vivo thrombus formation in mice. In addition, neither the guanylate cyclase inhibitor ODQ nor the adenylate cyclase inhibitor SQ22536 affected the amarogentin-mediated inhibition of platelet aggregation, which suggests that amarogentin does not regulate the levels of cyclic AMP and cyclic GMP. In conclusion, amarogentin prevents platelet activation through the inhibition of PLC γ2-PKC cascade and MAPK pathway. Our findings suggest that amarogentin may offer therapeutic potential for preventing or treating thromboembolic disorders.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenine; Adenosine Triphosphate; Animals; Arachidonic Acid; Collagen; Cyclic GMP; Guanylate Cyclase; Humans; Iridoids; MAP Kinase Signaling System; Mice; Oxadiazoles; Phospholipase C gamma; Plant Extracts; Platelet Activation; Protein Kinase C; Quinoxalines; Thrombin; Thromboembolism; Thrombosis

Inhaled nitric oxide (iNO) is a potent pulmonary vasodilator, but therapeutic experience in patients with severe pulmonary hypertension is scarce.. Eleven patients with severe pulmonary hypertension, 6 due to pulmonary arterial hypertension and 4 due to chronic thromboembolic disease, were selected for iNO therapy. A phosphodiesterase type 5 inhibitor (PDE5i) was added in cases of clinical worsening. In this study we evaluate the clinical effectiveness and safety of long-term treatment with iNO either alone or combined with a PDE5i.. After 1 month of iNO administration, improvements were observed in World Health Organization functional class, Borg scale (p = 0.003), brain natriuretic peptide levels (p = 0.002) and 6-minute walk test (p = 0.003). After 6 months of treatment, 7 patients had clinical deterioration that was reversed upon adding a PDE5i. One of these patients died in Month 8 and another underwent pulmonary transplantation in Month 9. The clinical condition of the remaining 9 patients was unchanged after 1 year. A second right catheterization showed improvement in mean pulmonary arterial pressure (66 +/- 15 mm Hg to 56 +/- 18 mm Hg; p = 0.01), pulmonary vascular resistance (1,234 +/- 380 dyn/s/cm(5) to 911 +/- 410 dyn/s/cm(5); p = 0.008) and cardiac index (2.0 +/- 0.4 liters/min/m(2) to 2.5 +/- 0.4 liters/min/m(2); p = 0.04). There was no significant increase in methemoglobin, no worsening of pulmonary function and no sudden withdrawal syndrome.. We suggest that iNO therapy alone or in combination with a PDE5i could be a therapeutic alternative for severe pulmonary hypertension.

Topics: Administration, Inhalation; Adult; Aged; Anticoagulants; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 5; Diuretics; Female; Follow-Up Studies; Humans; Hypertension, Pulmonary; Male; Middle Aged; Nitric Oxide; Phosphodiesterase 5 Inhibitors; Phosphodiesterase Inhibitors; Safety; Thromboembolism; Treatment Outcome; Vasodilator Agents

The aim of this study was to examine the inhibitory mechanisms of caffeic acid phenethyl ester (CAPE), which is derived from the propolis of honeybee, in platelet activation. In this study, CAPE (15 and 25 microM) markedly inhibited platelet aggregation stimulated by collagen (2 microg/ml). CAPE (15 and 25 microM) increased cyclic GMP level, and cyclic GMP-induced vasodilator-stimulated phosphoprotein (VASP) Ser157 phosphorylation, but did not increase cyclic AMP in washed human platelets. Rapid phosphorylation of a platelet protein of Mw. 47,000 (P47), a marker of protein kinase C activation, was triggered by phorbol-12, 13-dibutyrate (150 nM). This phosphorylation was markedly inhibited by CAPE (15 and 25 microM). The present study reports a novel and potent antiplatelet agent, CAPE, which involved in the following inhibitory pathways: CAPE increases cyclic GMP/VASP Ser157 phosphorylation, and subsequently inhibits protein kinase C activity, resulting in inhibition of P47 phosphorylation, which ultimately inhibits platelet aggregation. These results strongly indicate that CAPE appears to represent a novel and potent antiplatelet agent for treatment of arterial thromboembolism.

Topics: Blood Platelets; Caffeic Acids; Cell Adhesion Molecules; Cyclic AMP; Cyclic GMP; Humans; Microfilament Proteins; Phenylethyl Alcohol; Phorbol 12,13-Dibutyrate; Phosphoproteins; Phosphorylation; Platelet Activation; Platelet Aggregation; Platelet Aggregation Inhibitors; Protein Kinase C; Thromboembolism

Metallothionein (MT) is a low-molecular-weight, cysteine-rich protein that contains heavy metals such as cadmium and zinc. The biological function of MT in platelets is not yet understood. Therefore, the aim of this study was to systematically examine the inhibitory mechanisms of metallothionein in platelet aggregation. In this study, metallothionein concentration-dependently (1-8 microM) inhibited platelet aggregation in human platelets stimulated by agonists. Metallothionein (4 and 8 microM) inhibited phosphoinositide breakdown in [3H]-inositol-labeled platelets, intracellular Ca+2 mobilization in Fura-2 AM-loaded platelets, and thromboxane A2 formation stimulated by collagen. In addition, metallothionein (4 and 8 microM) significantly increased the formation of cyclic GMP but not cyclic AMP in human platelets. Rapid phosphorylation of a protein of Mr 47,000 (P47), a marker of protein kinase C activation, was triggered by PDBu (100 nM). This phosphorylation was markedly inhibited by metallothionein (4 and 8 microM) in phosphorus-32-labeled platelets. In an in vivo thrombotic study, platelet thrombus formation was induced by irradiation of mesenteric venules in mice pretreated with fluorescein sodium. Metallothionein (6 microg/g) significantly prolonged the latency period for inducing platelet plug formation in mesenteric venules. These results indicate that the antiplatelet activity of metallothionein may involve the following pathways: (1) metallothionein may inhibit the activation of phospholipase C, followed by inhibition of phosphoinositide breakdown and thromboxane A2 formation, thereby leading to inhibition of intracellular Ca+2 mobilization; (ii) Metallothionein also activated the formation of cyclic GMP in human platelets, resulting in inhibition of platelet aggregation. The results strongly indicate that metallothionein provides protection against thromboembolism.

Topics: Animals; Blood Platelets; Collagen; Cyclic AMP; Cyclic GMP; Humans; In Vitro Techniques; Metallothionein; Mice; Models, Biological; Phorbol 12,13-Dibutyrate; Phosphatidylinositols; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Protein Conformation; Signal Transduction; Thromboembolism; Thromboxane B2