Mechanisms involved in the antiplatelet activity of 8-methyl-4-(1-piperazinyl)-7-(3-pyridinylmethoxy)-2H-1-benzopyran-2-one (RC414)

The antithrombotic activity of natural and synthetic coumarins

Thrombosis, which seriously endangers human health and life, is the leading cause of morbidity and mortality globally. Antithrombotic drugs can interfere with the occurrence and development of thrombotic diseases and play an important role in the treatment of thrombotic diseases. However, unsatisfactory efficacy and serious adverse effects of existing antithrombotic drugs increase the research for new, efficient and safer drugs. Natural and synthetic coumarins have been shown to possess antithrombotic activity, namely, anticoagulation and antiplatelet aggregation. Especially, coumarin-based warfarin, phenprocoumon and cloricromen have long been used in clinical treatment of thrombosis. Coumarin with low toxicity is the privileged structure for developing novel antithrombotic drugs with multiple mechanisms of action. The present review aims to compile current research on the development of coumarins against thrombosis, emphasizing the relationship between their chemical structures and therapeutic effectiveness. It is intended to provide promising ideas for the discovery of novel coumarin derivatives with high antithrombotic activity.

Potential Antimigraine Effects of Warfarin: An Exploration of Biological Mechanism with Survey of Patients

Case reports suggest a link between anticoagulant use and improved migraine symptoms, and a role for platelet-induced cerebral vasoconstriction in migraine pathobiology. Hence, we investigated the mechanism by which warfarin may affect migraine symptoms and whether there is a change in migraine symptomology in patients initiating oral anticoagulants, most commonly warfarin. The effects of warfarin on human platelet aggregation and secretion as well as platelet-induced rat cerebral artery vasoconstriction were studied. A survey of migraine and symptom change after starting or stopping oral anticoagulants was also conducted. Warfarin inhibited platelet aggregation and 5-hydroxytryptamine (5-HT) secretion in a concentration-dependent manner. Warfarin-inhibited platelet secretion products constricted middle cerebral arteries from male but not from female rats. For the survey, patient demographic information, migraine and medical history, and Migraine Disability Assessment Score (MIDAS) changes were collected. Out of 175 consenting, 40 respondents met the criteria for migraine and completed the survey. A total of 11 patients reported migraine symptom change, all coinciding with starting warfarin. Of those having symptom and MIDAS improvement, most were female with migraines with aura, whereas those worsening were male with fewer having migraine with aura. Of those reporting migraine symptom change with warfarin, female sex may be associated with improved MIDAS, and those experiencing an aura component are more likely to report a symptom change. Warfarin-mediated symptom improvement in females may occur due to inhibition of platelet 5-HT secretion and a lower sensitivity of female cerebral blood vessels to platelet-derived 5-HT-induced vasoconstriction.

Regulation of cAMP Intracellular Levels in Human Platelets Stimulated by 2-Arachidonoylglycerol

We demonstrated that in human platelets the endocannabinoid 2-arachidonoylglycerol (2-AG) decreased dose- and time-dependently cAMP intracellular levels. No effect on cAMP decrease induced by 2-AG was observed in the presence of the adenylate cyclase inhibitor SQ22536 as well in platelets pretreated with the thromboxane A2 receptor antagonist, SQ29548 or with aspirin, inhibitor of arachidonic acid metabolism through the cyclooxygenase pathway. An almost complete recovering of cAMP level was measured in platelets pretreated with the specific inhibitor of phosphodiesterase (PDE) 3A, milrinone. In platelets pretreated with LY294002 or MK2206, inhibitors of PI3K/AKT pathway, and with U73122, inhibitor of phospholipase C pathway, only a partial prevention was shown. cAMP intracellular level depends on synthesis by adenylate cyclase and hydrolysis by PDEs. In 2-AG-stimulated platelets adenylate cyclase activity seems to be unchanged. In contrast PDEs appear to be involved. In particular PDE3A was specifically activated, as milrinone reversed cAMP reduction by 2-AG. 2-AG enhanced PDE3A activity through its phosphorylation. The PI3K/AKT pathway and PKC participate to this PDE3A phosphorylation/activation mechanism as it was greatly inhibited by platelet pretreatment with LY294002, MK2206, U73122, or the PKC specific inhibitor GF109203X. Taken together these data suggest that 2-AG potentiates its power of platelet agonist reducing cAMP intracellular level.

A review of the mechanisms and effectiveness of dietary polyphenols in reducing oxidative stress and thrombotic risk

Dietary sources of polyphenols, which are derivatives and/or isomers of flavones, isoflavones, flavonols, catechins and phenolic acids, possess antioxidant properties and therefore might be important in preventing oxidative-stress-induced platelet activation and attenuating adverse haemostatic function. Free radicals, including reactive oxygen and nitrogen species, promote oxidative stress, leading to platelet hyperactivation and the risk of thrombosis. The consumption of antioxidant/polyphenol rich foods might therefore impart anti-thrombotic and cardiovascular protective effects via their inhibition of platelet hyperactivation or aggregation. Most commonly-used anti-platelet drugs such as aspirin block the cyclooxygenase (COX)-1 pathway of platelet activation, similar to the action of antioxidants with respect to neutralising hydrogen peroxide (H2 O2 ), with a similar effect on thromboxane production via the COX-1 pathway. Polyphenols also target various additional platelet activation pathways (e.g. by blocking platelet-ADP, collagen receptors); thus alleviating fibrinogen binding to platelet surface (GPIIb-IIIa) receptors, reducing further platelet recruitment for aggregation and inhibiting platelet degranulation. As a result of the ability of polyphenols to target additional pathways of platelet activation, they may have the potential to substitute or complement currently used anti-platelet drugs in sedentary, obese, pre-diabetic or diabetic populations who can be resistant or sensitive to pharmacological anti-platelet therapy.

Synthesis, in vitro antiplatelet activity and molecular modelling studies of 10-substituted 2-(1-piperazinyl)pyrimido[1,2-a]benzimidazol-4(10H)-ones

The multistep preparation of the new 10-substituted 2-(1-piperazinyl)pyrimido[1,2-a]benzimidazol-4(10H)-ones 6a-o, and of the two isomers 10-ethyl-2-(diethylamino)pyrimido[1,2-a]benzimidazol-4(10H)-one 6p and 10-ethyl-4-(diethylamino)pyrimido[1,2-a]benzimidazol-2(10H)-one 13, as well as the in vitro evaluation of their inhibitory activity on human platelet aggregation induced in platelet-rich plasma by ADP, collagen or the Ca(2+) ionophore A23187 were here described. Nine out of fifteen 2-(1-piperazinyl)derivatives (6g-o) showed good inhibitory properties towards all the platelet aggregation agonists used. Moreover, a molecular modelling study has been performed on two of the best compounds of this series (6i and 6o) to confirm in silico their interactions with the catalytic site of human platelet PDE3, using the X-ray data of the PDE3B isoform in complex with an inhibitor.

In vitro platelet antiaggregatory properties of 4-methylcoumarins

Platelets play a crucial role in physiological haemostasis. However, in coronary arteries damaged by atherosclerosis, enhanced platelet aggregation, with subsequent thrombus formation, is a precipitating factor in acute myocardial infarction. Current therapeutic approaches are able to reduce approximately one quarter of cardiovascular events, but they are associated with an increased risk of bleeding and in some resistant patients are not efficient. Some coumarins possess antiplatelet activity and, due to their additional antioxidant effects, may be promising drugs for use in combination with the present therapeutic agents. The aim of this study was to analyse a series of simple 4-methylcoumarins for their antiplatelet activity. Human plasma platelet suspensions were treated with different aggregation inducers [arachidonic acid (AA), collagen and ADP] in the presence of the 4-methylcoumarins. Complementary experiments were performed to explain the mechanism of action. 5,7-Dihydroxy-4-methylcoumarins, in particular those containing a lipophilic side chain at C-3, reached the activity of acetylsalicylic acid on AA-induced aggregation. Other tested coumarins were less active. Some of the tested compounds mildly inhibited either collagen- or ADP-induced aggregation. 5,7-Dihydroxy-4-methylcoumarins did not interfere with the function of thromboxane synthase, but were competitive antagonists of thromboxane A(2) receptors and inhibited cyclooxygenase-1 as well. 5,7-Dihydroxy-4-methylcoumarins appear to be promising candidates for the extension of the current spectrum of antiplatelet drugs.

Mechanisms of lumbrokinase in protection of cerebral ischemia

The present study was designed to explore the mechanisms involved in the anti-ischemic action of lumbrokinase (LK) in brain. The enzyme immunoassay, spectrofluorimeter and flow cytometry were used to detect the level of adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP), the Ca(2+) mobilization, and human platelet surface antigen expression in order to elucidate the anti-platelet action involved in LK cerebroprotection. RT-PCR and western blot were used to identify the role of Intercellular adhesion molecule-1 (ICAM-1) and Janus Kinase1/Signal Transducers and Activators of Transcription1 (JAK1/STAT1) pathway in protecting brain against ischemic injury by anti-thrombosis and anti-apoptosis. Results showed that LK significantly potentiated the activity of adenylate cyclase (AC), increased the cAMP level in vivo, remarkably inhibited the rise of rat platelet intracellular Ca(2+) ([Ca(2+)](i)), and attenuated the expression of Glycoprotein IIB/IIIA (GPIIB/IIIA) and P-selectin in human platelet stimulated by thrombin in vitro. Furthermore, the expressions of ICAM-1 and JAK1/STAT1 were remarkably regulated by LK in Human Umbilical Vein Endothelial Cell (HUVEC) and ischemic cerebral tissues. These data indicated that the anti-ischemic activity of LK was due to its anti-platelet activity by elevating cAMP level and attenuating the calcium release from calcium stores, the anti-thrombosis action due to inhibiting of ICAM-1 expression, and the anti-apoptotic effect due to the activation of JAK1/STAT1 pathway.

Application of high-throughput screening to identify a novel alphaIIb-specific small- molecule inhibitor of alphaIIbbeta3-mediated platelet interaction with fibrinogen

Small-molecule alphaIIbbeta3 antagonists competitively block ligand binding by spanning between the D224 in alphaIIb and the MIDAS metal ion in beta3. They variably induce conformational changes in the receptor, which may have undesirable consequences. To identify alphaIIbbeta3 antagonists with novel structures, we tested 33 264 small molecules for their ability to inhibit the adhesion of washed platelets to immobilized fibrinogen at 16 muM. A total of 102 compounds demonstrated 50% or more inhibition, and one of these (compound 1, 265 g/mol) inhibited ADP-induced platelet aggregation (IC(50): 13+/- 5 muM), the binding of soluble fibrinogen to platelets induced by mAb AP5, and the binding of soluble fibrinogen and a cyclic RGD peptide to purified alphaIIbbeta3. Compound 1 did not affect the function of GPIb, alpha2beta1, or the other beta3 family receptor alphaVbeta3. Molecular docking simulations suggest that compound 1 interacts with alphaIIb but not beta3. Compound 1 induced partial exposure of an alphaIIb ligand-induced binding site (LIBS), but did not induce exposure of 2 beta3 LIBS. Transient exposure of purified alphaIIbbeta3 to eptifibatide, but not compound 1, enhanced fibrinogen binding ("priming"). Compound 1 provides a prototype for small molecule selective inhibition of alphaIIbbeta3, without receptor priming, via targeting alphaIIb.

Synthesis and in vitro antiplatelet activity of new 4-(1-piperazinyl)coumarin derivatives. Human platelet phosphodiesterase 3 inhibitory properties of the two most effective compounds described and molecular modeling study on their interactions with phosphodiesterase 3A catalytic site

The synthesis and in vitro antiplatelet activity significant data of coumarin derivatives 5i-x and quinolin-2(1H)-one derivatives 22a,b, as well as the corresponding structure-activity relationships are described. The recently reported 8-methyl-4-(1-piperazinyl)-7-(3-pyridylmethoxy)coumarin 5f and its potent 7-(2-morpholinoethoxy)-substituted new analogue 5u were notably more effective inhibitors of pure human platelet PDE3 than milrinone and cilostazol: these data were related, through a molecular modeling study, with the molecular interactions of the four compounds with the human PDE3A catalytic site.

Analysis of anti-PDE3 activity of 2-morpholinochromone derivatives reveals multiple mechanisms of anti-platelet activity

A series of synthetic 2-morpholinochromones have been evaluated as inhibitors of platelet phosphodiesterase, PDE3A. While previous assertions about the anti-PDE3 activity of this class have been confirmed, in some cases the reported anti-platelet activities clearly derive from a non-PDE3 regulated mechanism. The potential utility of 2-morpholinochromones either as PDE3 inhibitors and/or anti-thrombotic agents thus remains only poorly examined.

Synthesis and in vitro inhibitory activity on human platelet aggregation of novel properly substituted 4-(1-piperazinyl)coumarins

Pursuing our chemical and biological studies in this field, we described the multistep preparation of the new 5-, 6-, or 7-alkoxy and 7-alkoxy-8-methyl substituted 4-(1-piperazinyl)coumarins 5d-v, as well as the in vitro evaluation of their inhibitory activity on human platelet aggregation induced in platelet-rich plasma by ADP, collagen or the Ca(2+) ionophore A23187. Compounds 5h-j,p,r-u showed notably high activity towards all the platelet aggregation inducers used, and the most active one, 8-methyl-4-(1-piperazinyl)-7-(3-pyridylmethoxy)coumarin (5t), proved to be a potent in vitro antiplatelet agent.