Chlorogenic acid inhibits human platelet activation and thrombus formation

Synthesis of antiplatelet ortho-carbonyl hydroquinones with differential action on platelet aggregation stimulated by collagen or TRAP-6

Cardiovascular diseases are the leading cause of death in the world. Platelets have a major role in cardiovascular events as they bind to the damaged endothelium activating and forming thrombi. Although some hydroquinone scaffold-containing compounds have known antiplatelet activities, currently there is a lack of evidence on the antiplatelet activity of hydroquinones carrying electron attractor groups. In this work, we evaluate the antiplatelet effect of a series of ortho-carbonyl hydroquinone derivatives on cytotoxicity and function of human platelets, using collagen and thrombin receptor activator peptide 6 (TRAP-6) as agonists. Our structure-activity relationship study shows that gem-diethyl/methyl substitutions and the addition/modifications of the third ring of ortho-carbonyl hydroquinone scaffold influence on the selective index (IC₅₀ TRAP-6/IC₅₀ Collagen) and the inhibitory capacity of platelet aggregation. Compounds 3 and 8 inhibit agonist-induced platelet aggregation in a non-competitive manner with IC₅₀ values of 1.77 ± 2.09 μM (collagen) and 11.88 ± 4.59 μM (TRAP-6), respectively and show no cytotoxicity. Both compounds do not affect intracellular calcium levels and mitochondrial bioenergetics. Consistently, they reduce the expression of P-selectin, activation of glycoprotein IIb/IIIa, and release of adenosine triphosphate and CD63 from platelet. Our findings may be used for further development of new drugs in platelet-related thrombosis diseases.

Considerations for Docking of Selective Angiotensin-Converting Enzyme Inhibitors

The angiotensin-converting enzyme (ACE) is a two-domain dipeptidylcarboxypeptidase, which has a direct involvement in the control of blood pressure by performing the hydrolysis of angiotensin I to produce angiotensin II. At the same time, ACE hydrolyzes other substrates such as the vasodilator peptide bradykinin and the anti-inflammatory peptide N-acetyl-SDKP. In this sense, ACE inhibitors are bioactive substances with potential use as medicinal products for treatment or prevention of hypertension, heart failures, myocardial infarction, and other important diseases. This review examined the most recent literature reporting ACE inhibitors with the help of molecular modeling. The examples exposed here demonstrate that molecular modeling methods, including docking, molecular dynamics (MD) simulations, quantitative structure-activity relationship (QSAR), etc, are essential for a complete structural picture of the mode of action of ACE inhibitors, where molecular docking has a key role. Examples show that too many works identified ACE inhibitory activities of natural peptides and peptides obtained from hydrolysates. In addition, other works report non-peptide compounds extracted from natural sources and synthetic compounds. In all these cases, molecular docking was used to provide explanation of the chemical interactions between inhibitors and the ACE binding sites. For docking applications, most of the examples exposed here do not consider that: (i) ACE has two domains (nACE and cACE) with available X-ray structures, which are relevant for the design of selective inhibitors, and (ii) nACE and cACE binding sites have large dimensions, which leads to non-reliable solutions during docking calculations. In support of the solution of these problems, the structural information found in Protein Data Bank (PDB) was used to perform an interaction fingerprints (IFPs) analysis applied on both nACE and cACE domains. This analysis provides plots that identify the chemical interactions between ligands and both ACE binding sites, which can be used to guide docking experiments in the search of selective natural components or novel drugs. In addition, the use of hydrogen bond constraints in the S₂ and S₂′ subsites of nACE and cACE are suggested to guarantee that docking solutions are reliable.

Polyphenols: Modulators of Platelet Function and Platelet Microparticle Generation?

Platelets and platelet microparticles (PMPs) play a key role in the pathophysiology of vascular disorders such as coronary artery disease and stroke. In atherosclerosis, for example, the disruption of the plaque exposes endogenous agonists such as collagen, which activates platelets. Platelet hyper-activation and the high levels of PMPs generated in such situations pose a thrombotic risk that can lead to strokes or myocardial infarctions. Interestingly, dietary polyphenols are gaining much attention due to their potential to mimic the antiplatelet activity of treatment drugs such as aspirin and clopidogrel that target the glycoprotein VI (GPVI)-collagen and cyclooxygenease-1 (COX-1)-thromboxane platelet activation pathways respectively. Platelet function tests such as aggregometry and flow cytometry used to monitor the efficacy of antiplatelet drugs can also be used to assess the antiplatelet potential of dietary polyphenols. Despite the low bioavailability of polyphenols, several in vitro and dietary intervention studies have reported antiplatelet effects of polyphenols. This review presents a summary of platelet function in terms of aggregation, secretion, activation marker expression, and PMP release. Furthermore, the review will critically evaluate studies demonstrating the impact of polyphenols on aggregation and PMP release.

Characterization of active anticoagulant fraction and a fibrin(ogen)olytic serine protease from leaves of Clerodendrum colebrookianum, a traditional ethno-medicinal plant used to reduce hypertension

ETHNOPHARMACOLOGICAL RELEVANCE

Cardiovascular diseases are the major cause of mortality and morbidity, causing over 17.9 million deaths a year worldwide. Currently used therapy is often having side effects and expensive, dietary interventions and alternative medicines are required. Clerodendrum colebrookianum has been used to treat cardiac hypertension but anticoagulant potency was not evaluated.

AIM OF THE STUDY

To characterize an active anticoagulant fraction (AAFCC) and a 30 kDa fibrin(ogen)olytic serine protease (clerofibrase) isolated from aqueous leave extract of C. colebrookianum.

MATERIALS AND METHODS

AAFCC/clerofibrase was subjected to extensive biochemical and pharmacological characterization including LC-MS/MS, amino acid compositional and GC-MS analyses. Interaction between clerofibrase with fibrinogen was studied by spectrofluorometric analysis. In vitro thrombolytic, antiplatelet and cytotoxicity assay were performed. In vivo toxicity, anticoagulant, defibrinogen and antithrombotic activities were determined on Swiss albino mice.

RESULTS

The in vitro anticoagulant activity of AAFCC was found to be superior to heparin and clerofibrase and comparable to Nattokinase and warfarin. The proteomics and amino acid composition analyses suggest that clerofibrase is a previously uncharacterized novel plant protease capable of degrading the -αβ chains of fibrinogen/fibrin. AAFCC/clerofibrase exerts their anticoagulant action via fibrinogenolytic activity and partially by antiplatelet activity albeit they have no effect on thrombin and FXa inhibition. The spectrofluorometric analysis revealed the binding of clerofibrase to fibrinogen but not to thrombin and FXa. The phytochemical constituents and bioactive components of AAFCC were characterized by biochemical, and GC-MS analyses. The AAFCC and clerofibrase inhibited collagen/ADP-induced mammalian platelet aggregation, showed in vitro thrombolytic activity, and non-cytotoxic to mammalian cells. The AAFCC showed and dose-dependent in vivo plasma defibrinogenating and anticoagulant activities and inhibited k-carrageen-induced thrombus formation in the tails of mice.

CONCLUSION

The potent in vivo anticoagulant and antithrombotic effects of AAFCC suggests its pharmacological significance as herbal anticoagulant drug for the prevention and/or treatment of hyperfibrinogenemia- and thrombosis associated cardiovascular disorders.

Anti-aggregation effect on platelets of Indiplon a hypnotic sedative non-benzodiazepine drug

Cardiovascular diseases are one of the main public health problems, and many of them, their pathophysiology involves alterations in platelet activity. Platelet activation is an essential event that is regulated by the intracellular concentrations of Ca2+ and cAMP. Interestingly, it has been shown that the activation of adenosine A2A receptors increases cAMP levels and produces the inhibition of platelet aggregation, which appears as a potential target for regulation of platelet activity. Therefore, we tried to activate A2A receptors using Indiplon, a drug developed for the treatment of insomnia, and analyze its effect on platelet activity in vitro. Our results indicate that Indiplon is able to interact in silico with the adenosine A2A receptor (ΔG_bind of -73.321 kcal/mol, similar to that obtained with adenosine), which is involved in the regulation of platelet cAMP levels. In functional studies using PRP, a reduction in platelet aggregation induced by ADP was observed in the presence of Indiplon at 500 μM with a percentage of inhibition 70%, where the use of specific inhibitors (ZM241385 and MSX-2) of the A2A receptor also blocked these effects reducing the percentage of inhibition to 41% and 34.1%, respectively. Also, the use of Indiplon produced a decrease in the expression in the membrane of P-selectin. Thus, Indiplon acts as an A2A receptor agonist and whose activation results in inhibition of platelet aggregation and activation, showing a possible cardiovascular protective role.

The cAMP/PKA Pathway Inhibits Beta-amyloid Peptide Release from Human Platelets

The main component of Alzheimer's disease (AD) is the amyloid-beta peptide (Aβ), the brain of these patients is characterized by deposits in the parenchyma and cerebral blood vessels known as cerebral amyloid angiopathy (CAA). On the other hand, the platelets are the major source of the Aβ peptide in circulation and once secreted can activate the platelets and endothelial cells producing the secretion of several inflammatory mediators that finally end up unchaining the CAA and later AD. In the present study we demonstrate that cAMP/PKA pathway plays key roles in the regulation of calpain activation and secretion of Aβ in human platelets. We confirmed that inhibition of platelet functionality occurred when platelets were incubated with forskolin (molecule that rapidly increased cAMP levels). In this sense we found that platelets pre-incubated with forskolin (20 μM) present a complete inhibition of calpain activity and this effect is reversed using an inhibitor of protein kinase A. Consequentially, when platelets were inhibited by forskolin a reduction in the processing of the APP with the consequent decrease in the Aβ peptide secretion was observed. Therefore our study provides novel insight in relation to the mechanism of processing and release of the Aβ peptide from human platelets.

Coffee, caffeine, chlorogenic acid, and the purinergic system

Coffee is a drink prepared from roasted coffee beans and is lauded for its aroma and flavour. It is the third most popular beverage in the world. This beverage is known by its stimulant effect associated with the presence of methylxanthines. Caffeine, a purine-like molecule (1,3,7 trymetylxantine), is the most important bioactive compound in coffee, among others such as chlorogenic acid (CGA), diterpenes, and trigonelline. CGA is a phenolic acid with biological properties as antioxidant, anti-inflammatory, neuroprotector, hypolipidemic, and hypoglicemic. Purinergic system plays a key role inneuromodulation and homeostasis. Extracellular ATP, other nucleotides and adenosine are signalling molecules that act through their specific receptors, namely purinoceptors, P1 for nucleosides and P2 for nucleotides. They regulate many pathological processes, since adenosine, for instance, can limit the damage caused by ATP in the excitotoxicity from the neuronal cells. The primary purpose of this review is to discuss the effects of coffee, caffeine, and CGA on the purinergic system. This review focuses on the relationship/interplay between coffee, caffeine, CGA, and adenosine, and their effects on ectonucleotidases activities as well as on the modulation of P1 and P2 receptors from central nervous system and also in peripheral tissue.

Comparison of different microscopy approaches to quantification of inhibitory effect on thrombus formation under flow conditions by the example of adenosine receptor agonist HE-NECA

INTRODUCTION

Thrombus formation in vitro in flow conditions and its visualization and quantification with the use of microscopy are widely utilized to evaluate activity of compounds with a potential antithrombotic activity. Visualization and quantification of thrombi can be performed with the use of wide-field or confocal microscopy. Acquiring reliable numerical data from wide-field microscopy images of objects which have a complex three-dimensional structure is strongly influenced by the methods used for image analysis. This can be a possible source of inaccuracy in assessment of antithrombotic activity of a tested substance. We aimed to verify how different approaches to the quantification of wide-field images can affect the evaluation of an antiplatelet effect of a tested substance.

METHODS

We compared three algorithms of image analysis to evaluate an effect of 2-hexynyl-5'-ethylcarboxamidoadenosine (HE-NECA), a compound of a moderate antiplatelet activity on thrombus formation, and of abciximab - a potent antiplatelet compound. Also, we studied how the results obtained in a wide-field imaging correspond to those obtained by means of confocal imaging.

RESULTS

Three algorithms for analysis of wide-field images showed antiplatelet effect of HE-NECA or abciximab. Absolute values of thrombus area and outcomes of the evaluation of inhibition efficacy of HE-NECA were significantly different between the algorithms. Analysis of volumes and heights of thrombi obtained by confocal imaging confirmed inhibitory effect of HE-NECA, but the evaluated levels of inhibition were significantly different from that obtained by wide-field imaging.

DISCUSSION

We conclude that wide-field imaging provides reliable qualitative data on an inhibitory effect on thrombus formation, despite differences which can emerge from various approaches to image analysis. However, quantitative evaluation and comparison of the efficacy of inhibitors on the basis of total area occupied by thrombi obtained by wide-field microscopy should be made with caution. To obtain a reliable quantitative assessment of the effect of a tested compound on thrombus structure the use of confocal microscopy is inevitable.

Gintonin modulates platelet function and inhibits thrombus formation via impaired glycoprotein VI signaling

Panax ginseng (P. ginseng), one of the most valuable medicinal plants, is known for its healing and immunobooster properties and has been widely used in folk medicine against cardiovascular diseases, including stroke and heart attack. In this study, we explored the anti-platelet activity of gintonin (a recently discovered non-saponin fraction of ginseng) against agonist-induced platelet activation. In vitro effects of gintonin on agonist-induced human and rat platelet aggregation, granule secretion, integrin α_IIbβ₃ activation, and intracellular calcium ion ([Ca²⁺]_i) mobilization were examined. Western blot analysis and immunoprecipitation techniques were used to estimate the expression of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) and interaction of glycoprotein VI (GPVI) signaling pathway molecules such as Src family kinases (SFK), tyrosine kinase Syk, and PLCγ2. In vivo effects were studied using acute pulmonary thromboembolism model in mice. Gintonin remarkably inhibited collagen-induced platelet aggregation and suppressed granule secretion, [Ca²⁺]_i mobilization, and fibrinogen binding to integrin α_IIbβ₃ in a dose-dependent manner and clot retraction. Gintonin attenuated the activation of MAPK molecules and PI3K/Akt pathway. It also inhibited SFK, Syk, and PLCγ2 activation and protected mice from thrombosis. Gintonin inhibited agonist-induced platelet activation and thrombus formation through impairment in GPVI signaling molecules, including activation of SFK, Syk, PLCγ2, MAPK, and PI3K/Akt; suggesting its therapeutic potential against platelet related CVD.

Anticoagulant mechanism, pharmacological activity, and assessment of preclinical safety of a novel fibrin(ogen)olytic serine protease from leaves of Leucas indica

The harnessing of medicinal plants containing a plethora of bioactive molecules may lead to the discovery of novel, potent and safe therapeutic agents to treat thrombosis-associated cardiovascular diseases. A 35 kDa (m/z 34747.5230) serine protease (lunathrombase) showing fibrin(ogen)olytic activity and devoid of N- and O- linked oligosaccharides was purified from an extract of aqueous leaves from L. indica. The LC-MS/MS analysis, de novo sequencing, secondary structure, and amino acid composition determination suggested the enzyme’s novel characteristic. Lunathrombase is an αβ-fibrinogenase, demonstrating anticoagulant activity with its dual inhibition of thrombin and FXa by a non-enzymatic mechanism. Spectrofluorometric and isothermal calorimetric analyses revealed the binding of lunathrombase to fibrinogen, thrombin, and/or FXa with the generation of endothermic heat. It inhibited collagen/ADP/arachidonic acid-induced mammalian platelet aggregation, and demonstrated antiplatelet activity via COX-1 inhibition and the upregulation of the cAMP level. Lunathrombase showed in vitro thrombolytic activity and was not inhibited by endogenous protease inhibitors α₂ macroglobulin and antiplasmin. Lunathrombase was non-cytotoxic to mammalian cells, non-hemolytic, and demonstrated dose-dependent (0.125–0.5 mg/kg) in vivo anticoagulant and plasma defibrinogenation activities in a rodent model. Lunathrombase (10 mg/kg) did not show toxicity or adverse pharmacological effects in treated animals.

Effects of chlorogenic acid on carbachol-induced contraction of mouse urinary bladder

Chlorogenic acid (CGA) is a polyphenol found in coffee and medicinal herbs such as Lonicera japonica. In this study, the effect of CGA-induced relaxation on carbachol (CCh)-induced contraction of mouse urinary bladder was investigated. CGA (30-300 μg/ml) inhibited CCh- or U46619-induced contraction in a concentration-dependent manner. SQ22536 (adenylyl cyclase inhibitor) recovered CGA-induced relaxation of CCh-induced contraction; however, ODQ (guanylyl cyclase inhibitor) did not have the same effect. In addition, 3-isobutyl-1-methylxanthine (IBMX) enhanced CGA-induced relaxation; however, forskolin or sodium nitroprusside did not have the same effect. Moreover, Ro 20-1724, a selective phosphodiesterase (PDE) 4 inhibitor, enhanced CGA-induced relaxation, but vardenafil, a selective PDE5 inhibitor, did not have the same effect. In the presence of CCh, CGA increased cyclic adenosine monophosphate (cAMP) level, whereas SQ22536 inhibited the increase of cAMP levels. Moreover, higher cAMP levels were obtained with CGA plus IBMX treatment than the total cAMP levels obtained with separate CGA and IBMX treatments. In conclusion, these results suggest that CGA inhibited CCh-induced contraction of mouse urinary bladder by partly increasing cAMP levels via adenylyl cyclase activation.

Hydroxycinnamic acids loaded in lipid-core nanocapsules

Ferulic, caffeic, sinapic, and coumaric acids, belonging to the class of hydroxycinnamic acids (HAs), are bioactive polyphenols widespread in the plant kingdom and present in the human diet. Due to their biological properties and effects in the prevention of various diseases associated with oxidative stress, HAs can be exploited for attractive nutraceutical applications. Starting from this and in order to increase bioaccessibility, we encapsulated HAs in lipid-core nanocapsules (NCs) based on a biodegradable and biocompatible poly(ε-caprolactone) polymer. The results showed that nanoparticles loaded with hydroxycinnamic acids (HA-NCs) have diameter of 224-253 nm, encapsulation efficiency of 53-78%, and are stable over time (30 days). In vitro tests evidenced that NCs are able to preserve HAs in the gastric simulated fluid and release them in the intestinal simulated fluid. The delivery system developed could be employed to create novel functional foods.

Adenosine A2A receptor agonists with potent antiplatelet activity

Selected adenosine A_2A receptor agonists (PSB-15826, PSB-12404, and PSB-16301) have been evaluated as new antiplatelet agents. In addition, radioligand-binding studies and receptor-docking experiments were performed in order to explain their differential biological effects on a molecular level. Among the tested adenosine derivatives, PSB-15826 was the most potent compound to inhibit platelet aggregation (EC₅₀ 0.32 ± 0.05 µmol/L) and platelet P-selectin cell-surface localization (EC₅₀ 0.062 ± 0.2 µmol/L), and to increase intraplatelets cAMP levels (EC₅₀ 0.24 ± 0.01 µmol/L). The compound was more active than CGS21680 (EC₅₀ 0.97±0.07 µmol/L) and equipotent to NECA (EC₅₀ 0.31 ± 0.05 µmol/L) in platelet aggregation induced by ADP. In contrast to the results from cAMP assays, K_i values determined in radioligand-binding studies were not predictive of the A_2A agonists' antiplatelet activity. Docking studies revealed the key molecular determinants of this new family of adenosine A_2A receptor agonists: differences in activities are related to π-stacking interactions between the ligands and the residue His264 in the extracellular loop of the adenosine A_2A receptor which may result in increased residence times. In conclusion, these results provide an improved understanding of the requirements of antiplatelet adenosine A_2A receptor agonists.

The colonic metabolites dihydrocaffeic acid and dihydroferulic acid are more effective inhibitors of in vitro platelet activation than their phenolic precursors

Cardiovascular disease (CVD) is the major cause of morbidity and mortality worldwide. The consumption of a healthy diet rich in polyphenols has been inversely associated with the development of CVD. This study evaluated the effects of green coffee bean extract (GCBE) and yerba mate phenolic extract (YMPE), the main phenolic and methylxanthine constituents (5-caffeoylquinic acid, 3,5-dicaffeoylquinic acid, caffeine, and theobromine), and their main metabolites (caffeic acid, ferulic acid, dihydrocaffeic acid (DHCA) and dihydroferulic acid (DHFA)) on platelet activation in vitro. Upon incubation with different doses (0.01-100 μg mL-1 or μM) of each compound, adenosine 5'-diphosphate-induced P-selectin expression and fibrinogen binding were determined using whole blood flow cytometry. Platelet P-selectin expression was significantly decreased by YMPE and all phenolic and methylxanthine constituents at physiological concentrations, compared with control, whereas fibrinogen binding on platelets was significantly increased. The colonic metabolites (DHCA and DHFA) had stronger inhibitory effects on P-selectin expression than their phenolic precursors, suggesting an increase in the efficacy to modulate platelet activation with the metabolism of the phenolic compounds.

Investigation of the anticoagulant and antithrombotic effects of chlorogenic acid

Thrombosis is a leading cause of morbidity and mortality throughout the world. Thrombolytic agents are important for both the prevention and treatment of thrombosis. Fibrin clot and turbidity assays revealed that it was able to inhibit the formation of fibrin clot. Chlorogenic acid degraded blood clot and inhibited the enzymatic activity of procoagulant proteases, thrombin, activated factor X (FXa), and activated factor XIII (FXIIIa). Chlorogenic acid was found to delay activated partial thromboplastin time, prothrombin time, and thrombin time. PFA-100 assays showed that it prolonged the closure time of citrated whole human blood. It demonstrated the antithrombotic effect in collagen and epinephrine-induced acute thromboembolism mice model. These antithrombotic profiles together with its anticoagulant and platelet disaggregation properties, and lack of toxicity to NIH-3T3 and 3T3-L1 cells, make it a potential agent for thrombotic treatment and prevention.

Effects of chlorogenic acid, caffeine and coffee on components of the purinergic system of streptozotocin-induced diabetic rats

We evaluated the effect of chlorogenic acid (CGA), caffeine (CA) and coffee (CF) on components of the purinergic system from the cerebral cortex and platelets of streptozotocin-induced diabetic rats. Animals were divided into eight groups: control animals treated with (I) water (WT), (II) CGA (5 mg/kg), (III) CA (15 mg/kg) and (IV) CF (0.5 g/kg), and diabetic animals treated with (V) WT, (VI) CGA (5 mg/kg), (VII) CA (15 mg/kg) and (VIII) CF (0.5 g/kg). Our results showed an increase (173%) in adenosine monophosphate (AMP) hydrolysis in the cerebral cortex of diabetic rats. In addition, CF treatment increased adenosine diphosphate (ADP) and AMP hydrolysis in group VIII synaptosomes. Platelets showed an increase in ectonucleotidase activity in group V, and all treatments reduced the increase in adenosine triphosphate and ADP hydrolysis. Furthermore, there was an increase in platelet aggregation of 72% in the diabetic rats, and CGA and CF treatment reduced platelet aggregation by nearly 60% when compared to diabetic rats. In this context, we can suggest that CGA and CF treatment should be considered a therapeutic and scientific target to be investigated in diseases associated with hyperglycemia.

The Janus face of chlorogenic acid on vascular reactivity: A study on rat isolated vessels

BACKGROUND

Chlorogenic acid (CGA), the main polyphenol contained in coffee, is a major contributor to dietary polyphenol intake. Few studies reported its anti-hypertensive properties but the mechanisms are still indefinite.

PURPOSE

The present study assessed the direct effect of CGA in endothelium denuded or intact aortic rings from male Wistar rats and the mechanisms involved.

METHODS/RESULTS

CGA induced a direct endothelium-dependent relaxation that was significantly reduced by L-NAME (10(-4)M), indomethacin (10(-5)M) and combination of apamin (10(-7)M) and charybdotoxin (10(-7)M). Incubation of rings with CGA induced a dual effect on agonist-induced vasorelaxation. At 10(-6)M, it enhanced the relaxant effects of acetylcholine and reduced the contracting effects of phenylephrine due to increased basal and stimulated NOS activity, respectively. At 10(-4)M, CGA blunted acetylcholine and bradykinin-induced vasorelaxation, reduced phenylephrine-induced vasoconstriction but did not change the response to sodium nitroprusside, a NO-donor.

CONCLUSION

In summary, CGA induces a direct endothelium-dependent vasodilation by increasing NOS, COX and EDHF signalling pathways. However, this new pharmacological action that can explain some positive effects of CGA in case of hypertension has to be modulated at the light of its deleterious impact on vascular relaxation at high concentrations and incite to be cautious when using high doses of CGA in clinical studies.

NF-κB signaling pathway as target for antiplatelet activity

In different nucleated cells, NF-κB has long been considered a prototypical proinflammatory signaling pathway with the expression of proinflammatory genes. Although platelets lack a nucleus, a number of functional transcription factors are involved in activated platelets, such as NF-κB. In platelet activation NF-κB regulation events include IKKβ phosphorylation, IκBα degradation, and p65 phosphorylation. Multiple pathways contribute to platelet activation and NF-κB is a common pathway in this activation. Therefore, in platelet activation the modulation of NF-κB pathway could be a potential new target in the treatment of inflammation-related vascular disease therapy (antiplatelet and antithrombotic activities).

Delineation of Platelet Activation Pathway of Scutellarein Revealed Its Intracellular Target as Protein Kinase C

Erigeron breviscapus has been widely used in traditional Chinese medicine (TCM) and its total flavonoid component is commonly used to treat ischemic stroke, coronary heart disease, diabetes and hypertension. Scutellarin is the major ingredient of E. breviscapus and scutellarein is one of the main bioactive metabolites of scutellarin in vivo, but the latter's pharmacological activities have not been fully characterized. Provided evidence that could inhibit platelet aggregation, the effect of scutellarein on rat washed platelets and its underlying mechanisms were evaluated in our research. Scutellarein inhibited platelet adhesion and aggregation induced by multiple G protein coupled receptor agonists such as thrombin, U46619 and ADP, in a concentration-dependent manner. Furthermore, the mild effect of scutellarein on intracellular Ca(2+) mobilization and cyclic AMP (cAMP) level was observed. On the other hand, the role of scutellarein as potential protein kinase C (PKC) inhibitor was confirmed by PKC activity analysis and molecular docking. The phorbol myristate acetate-induced platelets aggregation assay with or without ADP implied that the scutellarein takes PKC(s) as its primary target(s), and acts on it in a reversible way. Finally, scutellarein as a promising agent exhibited a high inhibition effect on ADP-induced platelet aggregation among its analogues. This study clarifies the PKC-related signaling pathway involved in antiplatelet action of scutellarein, and may be beneficial for the treatment of cardiovascular diseases.

Therapeutic Potential of Dietary Phenolic Acids

Although modern lifestyle has eased the quality of human life, this lifestyle's related patterns have imparted negative effects on health to acquire multiple diseases. Many synthetic drugs are invented during the last millennium but most if not all of them possess several side effects and proved to be costly. Convincing evidences have established the premise that the phytotherapeutic potential of natural compounds and need of search for novel drugs from natural sources are of high priority. Phenolic acids (PAs) are a class of secondary metabolites spread throughout the plant kingdom and generally involved in plethora of cellular processes involved in plant growth and reproduction and also produced as defense mechanism to sustain various environmental stresses. Extensive research on PAs strongly suggests that consumption of these compounds hold promise to offer protection against various ailments in humans. This paper focuses on the naturally derived PAs and summarizes the action mechanisms of these compounds during disease conditions. Based on the available information in the literature, it is suggested that use of PAs as drugs is very promising; however more research and clinical trials are necessary before these bioactive molecules can be made for treatment. Finally this review provides greater awareness of the promise that natural PAs hold for use in the disease prevention and therapy.

Chloroform fraction of Euphorbia maculata has antiplatelet activity via suppressing thromboxane B2 formation

Euphorbia maculata (EM) is a traditionally used antidiarrheal, antibacterial, antifungal and antioxidant agent. However, the effects of EM on platelet activity remain to be elucidated. Therefore, the present study investigated the antiplatelet effect of various EM extract fractions on platelet aggregation in rats. The antiplatelet activity of the EM fractions on collagen or adenosine diphosphate (ADP)‑induced platelet aggregation was evaluated in vitro and ex vivo. Thromboxane B2 (TXB2) formation, rat‑tail bleeding time and coagulation time were also measured. Among the fractions, the chloroform fraction of EM (CFEM) significantly inhibited ADP‑induced platelet aggregation in vitro. Furthermore, oral administration of 50 mg/kg CFEM to rats significantly reduced ADP‑induced platelet aggregation without increasing the tail bleeding time or coagulation time. In addition, EM significantly inhibited the level of TXB2 formation in a dose‑dependent manner. These results suggest that CFEM exhibits antiplatelet activity, without causing bleeding, via the suppression of TXB2 formation. CFEM may be a type of food which has the potential for preventing cardiovascular disease.

Inhibitory effects of Cyperus digitatus extract on human platelet function in vitro

The purpose of this research was to investigate the mechanisms of antiplatelet action of Cyperus digitatus. The antiplatelet action of C. digitatus was studied on platelet function: secretion, adhesion, aggregation, and sCD40L release. The platelet ATP secretion and aggregation were significantly inhibited by CDA (ethyl acetate extract) at 0.1 mg/ml and after the incubation of whole blood with CDA, the platelet coverage was inhibited by 96 ± 3% (p < 0.001). At the same concentration, CDA significantly decreased sCD40L levels. The mechanism of antiplatelet action of CDA could be by NF-κB inhibition and that is cAMP independent. In conclusion, C. digitatus extract may serve as a new source of antiplatelet agents for food and nutraceutical applications.

Regulatory mechanisms of cAMP levels as a multiple target for antiplatelet activity and less bleeding risk

Platelet activation is a critical component of atherothrombosis. The multiple pathways of platelet activation limit the effect of specific receptor/pathway inhibitors, resulting in limited clinical efficacy. Recent research has confirmed that combination therapy results in enhanced antithrombotic efficacy without increasing bleeding risk. In this way, the best-known inhibitor and turn off signaling in platelet activation is cAMP. In this article we discuss the mechanisms of regulation of intraplatelet cAMP levels, a) platelet-dependent pathway: Gi/Gs protein-coupled receptors, phosphodiesterase inhibition and activation of PPARs and b) platelet-independent pathway: inhibition of adenosine uptake by erythrocytes. With respect to the association between intraplatelet cAMP levels and bleeding risk it is possible to establish that compounds/drugs with pleitropic effect for increased intraplatelet cAMP level could have an antithrombotic activity with less risk of bleeding.