Quercetin inhibits collagen-stimulated platelet activation through inhibition of multiple components of the glycoprotein VI signaling pathway

Studies on in vivo antithrombotic activity of quercetin, a natural flavonoid isolated from a traditional medicinal plant, African eggplant (Solanum indicum)

ETHNOPHARMACOLOGICAL RELEVANCE

Every year, cardiovascular diseases (CVDs) account for about 17.9 million deaths, making them the primary cause of both morbidity and mortality. Conventional drugs, which are often prescribed to treat cardiovascular diseases, are costly and have adverse effects. Consequently, dietary modifications and other medications are needed. Traditional use of Solanum indicum as cardiotonic to treat hypertension and anticoagulant potency has been reported but poorly evaluated scientifically.

AIM OF THE STUDY

This study investigated the in vivo anticoagulant activity and mechanism of anticoagulation of quercetin (QC), a bioactive compound isolated from S. indicum (SI) hydroethanolic fruit extract.

MATERIALS AND METHODS

Bioassay-guided fractionation (anticoagulant activity) extracted QC from hydroethanolic SI extract. QC was extensively characterized biochemically and pharmacologically. The interaction between QC and thrombin was investigated using spectrofluorometric and isothermal calorimetric methods. Cytotoxicity, antiplatelet, and thrombolytic studies were carried out in vitro. The Swiss albino mice were used to assess the in vivo, anticoagulant, and antithrombotic activities of QC.

RESULTS

QC exhibits anticoagulant activity via (i) uncompetitive inhibition of thrombin but not FXa with a Ki value of 33.11 ± 4.2 μM and (ii) a partial inhibition of thrombin-catalyzed platelet aggregation with an IC50 value of 13.2 ± 1.2 μM. The experimental validation of the in silico study's prediction of QC's binding to thrombin was confirmed by spectrofluorometric and isothermal calorimetric analyses. QC was nontoxic to mammalian, non-hemolytic cells and demonstrated thrombolytic activity by activating plasminogen. QC demonstrated in vivo anticoagulant efficacy, preventing k-carrageen-induced thrombus formation in mice's tails. In the acute circulatory stasis paradigm in mice, QC reduces thromboxane B2 (TXB2) and endothelin-1 (ET-1) while increasing nitric oxide synthase (eNOS) and 6-keto prostaglandin F1α (6-keto-PGF1 α).

CONCLUSION

Effective in vivo anticoagulant and antithrombotic properties of S. indicum's bioactive component QC point to the plant's potential use as a herbal anticoagulant medication for preventing and treating cardiovascular diseases linked to thrombosis.

Therapeutic effects and molecular mechanisms of natural products in thrombosis

Thrombotic disorders, such as myocardial infarction and stroke, are the leading cause of death in the global population and have become a health problem worldwide. Drug therapy is one of the main antithrombotic strategies, but antithrombotic drugs are not completely safe, especially the risk of bleeding at therapeutic doses. Recently, natural products have received widespread interest due to their significant efficacy and high safety, and an increasing number of studies have demonstrated their antithrombotic activity. In this review, articles from databases, such as Web of Science, PubMed, and China National Knowledge Infrastructure, were filtered and the relevant information was extracted according to predefined criteria. As a result, more than 100 natural products with significant antithrombotic activity were identified, including flavonoids, phenylpropanoids, quinones, terpenoids, steroids, and alkaloids. These compounds exert antithrombotic effects by inhibiting platelet activation, suppressing the coagulation cascade, and promoting fibrinolysis. In addition, several natural products also inhibit thrombosis by regulating miRNA expression, anti-inflammatory, and other pathways. This review systematically summarizes the natural products with antithrombotic activity, including their therapeutic effects, mechanisms, and clinical applications, aiming to provide a reference for the development of new antithrombotic drugs.

Plant Polyphenols and Their Potential Benefits on Cardiovascular Health: A Review

Fruits, vegetables, and other food items contain phytochemicals or secondary metabolites which may be considered non-essential nutrients but have medicinal importance. These dietary phytochemicals exhibit chemopreventive and therapeutic effects against numerous diseases. Polyphenols are secondary metabolites found in vegetables, fruits, and grains. These compounds exhibit several health benefits such as immune modulators, vasodilators, and antioxidants. This review focuses on recent studies on using dietary polyphenols to treat cardiovascular disorders, atherosclerosis, and vascular endothelium deficits. We focus on exploring the safety of highly effective polyphenols to ensure their maximum impact on cardiac abnormalities and discuss recent epidemiological evidence and intervention trials related to these properties. Kaempferol, quercetin, and resveratrol prevent oxidative stress by regulating proteins that induce oxidation in heart tissues. In addition, polyphenols modulate the tone of the endothelium of vessels by releasing nitric oxide (NO) and reducing low-density lipoprotein (LDL) oxidation to prevent atherosclerosis. In cardiomyocytes, polyphenols suppress the expression of inflammatory markers and inhibit the production of inflammation markers to exert an anti-inflammatory response. Consequently, heart diseases such as strokes, hypertension, heart failure, and ischemic heart disease could be prevented by dietary polyphenols.

Manjari Medika Grape Seed Extract Protects Methotrexate-Induced Hepatic Inflammation: Involvement of NF-κB/NLRP3 and Nrf2/HO-1 Signaling System

Objective

Grape Seed Extract is a natural source of various polyphenols, which have been shown to possess potent antioxidant and free radical-scavenging activities. The earlier studies have reported that grape seed extract exhibits broad-spectrum pharmacological activities. Therefore, studying the hepatoprotective effects and elucidation of mechanisms of action of the Indian Variety, Manjari Medika grape seed extract (GSE), may give an insight into therapeutic benefits. Methotrexate (MTX) is the first-line pharmacological therapy for different rheumatic diseases. The major adverse events such as hepatotoxicity are evident even in the low doses used for the treatment. The present study investigated the role of MTX on hepatic damage in murine liver and the plausible protective effects of the Indian grape variety, Manjari Medika grape seed extract, in ameliorating it.

Methods and Results

To assess the hepatological modulation, mice were divided into eight groups to investigate the ameliorative potential of this GSE (75 and 125 mg/kg) and correlate the experimental findings. The active components of the extract were assessed through UPLC-(ESI)-QToF-MS analysis. On the other hand, various biochemical and immunological indices were carried out to correlate the experimental data. The result demonstrated that the prophylactic administration of GSE reduced MTX-induced hepatic toxicity indices, which subsequently restored the hepatic morphological architecture. Moreover, the application of GSE in a dual dosage (75 and 125 mg/kg) suppressed MTX-induced reactive oxygen species generation, followed by lipid peroxidation and cellular nitrite formation. MTX-induced inflammasome activation through the redox-assisted cascade of TLR4/NF-κB signaling was further reduced by applying the GSE. The results showed that the activation of cytoprotective transcription factor Nrf2 enhanced the level of endogenous antioxidants. Furthermore, through the regulation of TLR4/NF-κB and Nrf2/HO-1 axis, this extract could reduce the MTX-mediated hepatic damage.

Conclusion

Our findings suggest that Manjari Medika seed extract could be used as a therapeutic agent to relieve the side effects of MTX and other hepatic disorders.

An optimized herbal medicine containing Scutellaria baicalensis Georgi, Alisma orientale Juzepzuk, and Atractylodes japonica Koidzumi has potent antiplatelet and antithrombotic activities

Background and aim

Platelet-derived thrombosis is important in the pathogenesis of cardiovascular diseases. HTB is an optimized herbal medicine including Scutellaria baicalensis Georgi, Alisma orientale Juzepzuk, and Atractylodes japonica Koidzumi. It is widely used in traditional medicine due to its anti-inflammatory and antioxidant effects. However, its antiplatelet and antithrombotic activities have not been completely validated. The current study aimed to examine the inhibitory effect of the novel herb formula HTB against platelet activation and thrombus formation.

Experimental procedure

The antiplatelet activities of HTB via platelet aggregation, granule secretion, reactive oxygen species generation, and intracellular calcium mobilization were evaluated. Moreover, the antithrombotic effect of HTB via FeCl₃-induced arterial thrombus formation in vivo in mice was assessed. The inhibitory effect of HTB against primary hemostasis was investigated based on transection tail bleeding time.

Results and conclusion

HTB treatment significantly inhibited glycoprotein VI-mediated platelet aggregation, granule secretion, reactive oxygen species generation, and intracellular calcium mobilization. Biochemical studies revealed that HTB inhibited glycoprotein VI-mediated platelet signal transduction during cell activation. Further, its antioxidant effect might be derived by reducing the phosphorylation of the p47^phox/Hic5 axis signalosome. Oral HTB treatment was effective in decreasing FeCl₃-induced arterial thrombus formation without prolonging the tail bleeding time. HTB can be an effective therapeutic agent against thrombotic diseases.

A Comprehensive Literature Review on Cardioprotective Effects of Bioactive Compounds Present in Fruits of Aristotelia chilensis Stuntz (Maqui)

Some fruits and vegetables, rich in bioactive compounds such as polyphenols, flavonoids, and anthocyanins, may inhibit platelet activation pathways and therefore reduce the risk of suffering from CVD when consumed regularly. Aristotelia chilensis Stuntz (Maqui) is a shrub or tree native to Chile with outstanding antioxidant activity, associated with its high content in anthocyanins, polyphenols, and flavonoids. Previous studies reveal different pharmacological properties for this berry, but its cardioprotective potential has been little studied. Despite having an abundant composition, and being rich in bioactive products with an antiplatelet role, there are few studies linking this berry with antiplatelet activity. This review summarizes and discusses relevant information on the cardioprotective potential of Maqui, based on its composition of bioactive compounds, mainly as a nutraceutical antiplatelet agent. Articles published between 2000 and 2022 in the following bibliographic databases were selected: PubMed, ScienceDirect, and Google Scholar. Our search revealed that Maqui is a promising cardiovascular target since extracts from this berry have direct effects on the reduction in cardiovascular risk factors (glucose index, obesity, diabetes, among others). Although studies on antiplatelet activity in this fruit are recent, its rich chemical composition clearly shows that the presence of chemical compounds (anthocyanins, flavonoids, phenolic acids, among others) with high antiplatelet potential can provide this berry with antiplatelet properties. These bioactive compounds have antiplatelet effects with multiple targets in the platelet, particularly, they have been related to the inhibition of thromboxane, thrombin, ADP, and GPVI receptors, or through the pathways by which these receptors stimulate platelet aggregation. Detailed studies are needed to clarify this gap in the literature, as well as to specifically evaluate the mechanism of action of Maqui extracts, due to the presence of phenolic compounds.

Neuroprotective Effects of Quercetin on Ischemic Stroke: A Literature Review

Ischemic stroke (IS) is characterized by high recurrence and disability; however, its therapies are very limited. As one of the effective methods of treating acute attacks of IS, intravenous thrombolysis has a clear time window. Quercetin, a flavonoid widely found in vegetables and fruits, inhibits immune cells from secreting inflammatory cytokines, thereby reducing platelet aggregation and limiting inflammatory thrombosis. In pre-clinical studies, it has been shown to exhibit neuroprotective effects in patients with ischemic brain injury. However, its specific mechanism of action remains unknown. Therefore, this review aims to use published data to elucidate the potential value of quercetin in patients with ischemic brain injury. This article also reviews the plant sources, pharmacological effects, and metabolic processes of quercetin in vivo, thus focusing on its mechanism in inhibiting immune cell activation and inflammatory thrombosis as well as promoting neuroprotection against ischemic brain injury.

Treatment of COVID-19 patients with quercetin: a prospective, single center, randomized, controlled trial

Scientific research continues on new preventive and therapeutic strategies against severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). So far, there is no proven curative treatment, and a valid alternative therapeutic approach needs to be developed. This study is designed to evaluate the effect of quercetin in COVID-19 treatment. This was a single-centre, prospective randomized controlled cohort study. Routine care versus QCB (quercetin, vitamin C, bromelain) supplementation was compared between 429 patients with at least one chronic disease and moderate-to-severe respiratory symptoms. Demographic features, signs, laboratory results and drug administration data of patients were recorded. The endpoint was that QCB supplementation was continued throughout the follow-up period from study baseline to discharge, intubation, or death. The most common complaints at the time of hospital admission were fatigue (62.4%), cough (61.1%), anorexia (57%), thirst (53.7%), respiratory distress (51%) and chills (48.3%). The decrease in CRP and ferritin levels was higher in the QCB group (all Ps were < 0.05). In the QCB group, the increase in platelet and lymphocyte counts was higher (all Ps were < 0.05). QCB did not reduce the risk of events during follow-up. Adjustments for statistically significant parameters, including the lung stage, use of favipiravir and presence of comorbidity did not change the results. While there was no difference between the groups in terms of event frequency, the QCB group had more advanced pulmonary findings. QCB supplement is shown to have a positive effect on laboratory recovery. While there was no difference between the groups in terms of event frequency, QCB supplement group had more advanced pulmonar findings, and QCB supplement is shown to have a positive effect on laboratory recovery/results. Therefore, we conclude that further studies involving different doses and plasma level measurements are required to reveal the dose/response relationship and bioavailability of QCB for a better understanding of the role of QCB in the treatment of SARS CoV-2.

Phenolic Bioactives as Antiplatelet Aggregation Factors: The Pivotal Ingredients in Maintaining Cardiovascular Health

Cardiovascular diseases (CVD) are one of the main causes of mortality in the world. The development of these diseases has a specific factor-alteration in blood platelet activation. It has been shown that phenolic compounds have antiplatelet aggregation abilities and a positive impact in the management of CVD, exerting prominent antioxidant, anti-inflammatory, antitumor, cardioprotective, antihyperglycemic, and antimicrobial effects. Thus, this review is intended to address the antiplatelet activity of phenolic compounds with special emphasis in preventing CVD, along with the mechanisms of action through which they are able to prevent and treat CVD. In vitro and in vivo studies have shown beneficial effects of phenolic compound-rich plant extracts and isolated compounds against CVD, despite that the scientific literature available on the antiplatelet aggregation ability of phenolic compounds in vivo is scarce. Thus, despite the current advances, further studies are needed to confirm the cardioprotective potential of phenolic compounds towards their use alone or in combination with conventional drugs for effective therapeutic interventions.

Flavonoids as potential anti-platelet aggregation agents: from biochemistry to health promoting abilities

Cardiovascular ailments are the number one cause of mortalities throughout the globe with 17.9 million deaths per year. Platelet activation and aggregation play a crucial role in the pathogenesis of arterial diseases, including acute coronary syndrome, acute myocardial infarction, cerebrovascular transient ischemia, unstable angina, among others. Flavonoids-rich plant extracts are gaining interest for treating the heart-related problems due to safe nature of these herbal extracts. Consumption of plant-food-derived bioactives, particularly flavonoids, has shown antithrombotic, and cardiovascular protective effects due to its anti-platelet activity. Preclinical and clinical trials have proven that flavonoid-rich plant extracts are protective against the cardiac ailments through anti-platelet aggregation activity. This review aims to highlight the anti-platelet aggregation potential of flavonoids with a key emphasis on the therapeutic efficacy in humans. The mechanism of flavonoids in preventing and treating cardiovascular diseases is also highlighted based on preclinical and clinical experimental trials. Further studies are the need of time for exploring the exact molecular mechanism of flavonoids as anti-platelet aggregation agents for treating heart-related problems.

Quercetin: A promising phytochemical for the treatment of glioblastoma multiforme

Quercetin, a plant-derived flavonoid, is known for its antitumor and antiproliferative activities. Glioblastoma multiforme (GBM), as a highly aggressive cerebrum tumor, has a poor prognosis that is approximately 12 months despite standard therapy. Therefore, because of the low effectiveness of the current therapeutic strategies, additional medications in combination with chemotherapy and radiotherapy are needed, which could improve the prognosis of GBM patients. Multiple lines of evidence have shown that quercetin regulates many proteins involved in the cellular signal transduction in GBM. In this review, recent findings on the targeting of particular signaling pathways by quercetin and the subsequent effect on the pathogenesis of GBM are presented and discussed.

Isorhapontigenin, a resveratrol analogue selectively inhibits ADP-stimulated platelet activation

Isorhapontigenin is a polyphenolic compound found in Chinese herbs and grapes. It is a methoxylated analogue of a stilbenoid, resveratrol, which is well-known for its various beneficial effects including anti-platelet activity. Isorhapontigenin possesses greater oral bioavailability than resveratrol and has also been identified to possess anti-cancer and anti-inflammatory properties. However, its effects on platelet function have not been reported previously. In this study, we report the effects of isorhapontigenin on the modulation of platelet function. Isorhapontigenin was found to selectively inhibit ADP-induced platelet aggregation with an IC₅₀ of 1.85 μM although it displayed marginal inhibition on platelet aggregation induced by other platelet agonists at 100 μM. However, resveratrol exhibited weaker inhibition on ADP-induced platelet aggregation (IC₅₀ > 100 μM) but inhibited collagen induced platelet aggregation at 50 μM and 100 μM. Isorhapontigenin also inhibited integrin αIIbβ3 mediated inside-out and outside-in signalling and dense granule secretion in ADP-induced platelet activation but interestingly, no effect was observed on α-granule secretion. Isorhapontigenin did not exert any cytotoxicity on platelets at the concentrations of up to 100 μM. Furthermore, it did not affect haemostasis in mice at the IC₅₀ concentration (1.85 μM). In addition, the mechanistic studies demonstrated that isorhapontigenin increased cAMP levels and VASP phosphorylation at Ser157 and decreased Akt phosphorylation. This suggests that isorhapontigenin may interfere with cAMP and PI3K signalling pathways that are associated with the P2Y₁₂ receptor. Molecular docking studies emphasised that isorhapontigenin has greater binding affinity to P2Y₁₂ receptor than resveratrol. Our results demonstrate that isorhapontigenin has selective inhibitory effects on ADP-stimulated platelet activation possibly via P2Y₁₂ receptor.

The Metabolites of the Dietary Flavonoid Quercetin Possess Potent Antithrombotic Activity, and Interact with Aspirin to Enhance Antiplatelet Effects

Quercetin, a dietary flavonoid, has been reported to possess antiplatelet activity. However, its extensive metabolism following ingestion has resulted in difficulty elucidating precise mechanisms of action. In this study, we aimed to characterize the antiplatelet mechanisms of two methylated metabolites of quercetin-isorhamnetin and tamarixetin-and explore potential interactions with aspirin. Isorhamnetin and tamarixetin inhibited human platelet aggregation, and suppressed activatory processes including granule secretion, integrin αIIbβ3 function, calcium mobilization, and spleen tyrosine kinase (Syk)/linker for activation of T cells (LAT) phosphorylation downstream of glycoprotein VI with similar potency to quercetin. All three flavonoids attenuated thrombus formation in an in vitro microfluidic model, and isoquercetin, a 3-O-glucoside of quercetin, inhibited thrombosis in a murine laser injury model. Isorhamnetin, tamarixetin, and quercetin enhanced the antiplatelet effects of aspirin more-than-additively in a plate-based aggregometry assay, reducing aspirin IC ₅₀ values by an order of magnitude, with this synergy maintained in a whole blood test of platelet function. Our data provide mechanistic evidence for the antiplatelet activity of two quercetin metabolites, isorhamnetin and tamarixetin, and suggest a potential antithrombotic role for these flavonoids. In combination with their interactions with aspirin, this may represent a novel avenue of investigation for the development of new antithrombotic strategies and management of current therapies.

Synthetic Flavonoids as Novel Modulators of Platelet Function and Thrombosis

Cardiovascular diseases represent a major cause of mortality and morbidity in the world, and specifically, thrombotic conditions such as heart attacks and strokes are caused by unwarranted activation of platelets and subsequent formation of blood clots (thrombi) within the blood vessels during pathological circumstances. Therefore, platelets act as a primary therapeutic target to treat and prevent thrombotic conditions. Current treatments are limited due to intolerance, and they are associated with severe side effects such as bleeding complications. Hence, the development of novel therapeutic strategies for thrombotic diseases is an urgent priority. Flavonoids are naturally occurring plant-derived molecules that exert numerous beneficial effects in humans through modulating the functions of distinct cell types. However, naturally occurring flavonoids suffer from several issues such as poor solubility, lipophilicity, and bioavailability, which hinder their efficacy and potency. Despite these, flavonoids act as versatile templates for the design and synthesis of novel molecules for various therapeutic targets. Indeed, several synthetic flavonoids have recently been developed to improve their stability, bioavailability, and efficacy, including for the modulation of platelet function. Here, we provide insight into the actions of certain natural flavonoids along with the advantages of synthetic flavonoids in the modulation of platelet function, haemostasis, and thrombosis.

Roles of Phenolic Compounds in the Reduction of Risk Factors of Cardiovascular Diseases

The population is now living longer during the period classified as "elderly" (60 years and older), exhibiting multimorbidity associated to the lengthening of the average life span. The dietary intake of phenolic compounds (PC) may affect the physiology, disease development and progression during the aging process, reducing risk factors of age related diseases. The aim of this review is to briefly describe some of the possible effects of a series of PC on the reduction of risk factors of the onset of cardiovascular diseases, considering their potential mechanisms of action. The main actions described for PC are associated with reduced platelet activity, anti-inflammatory effects, and the protection from oxidation to reduce LDL and the generation of advanced glycation end products. Preclinical and clinical evidence of the physiological effects of various PC is presented, as well as the health claims approved by regulatory agencies.

Cardiovascular Effects of Flavonoids

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Cardiovascular Disease (CVD) is the major cause of death worldwide, especially in Western society. Flavonoids are a large group of polyphenolic compounds widely distributed in plants, present in a considerable amount in fruit and vegetable. Several epidemiological studies found an inverse association between flavonoids intake and mortality by CVD. The antioxidant effect of flavonoids was considered the main mechanism of action of flavonoids and other polyphenols. In recent years, the role of modulation of signaling pathways by direct interaction of flavonoids with multiple protein targets, namely kinases, has been increasingly recognized and involved in their cardiovascular protective effect. There are strong evidence, in in vitro and animal experimental models, that some flavonoids induce vasodilator effects, improve endothelial dysfunction and insulin resistance, exert platelet antiaggregant and atheroprotective effects, and reduce blood pressure. Despite interacting with multiple targets, flavonoids are surprisingly safe. This article reviews the recent evidence about cardiovascular effects that support a beneficial role of flavonoids on CVD and the potential molecular targets involved.

Flavonoids and Platelet-Derived Thrombotic Disorders

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Thrombotic disorders are characterized by an increase in the probability of the formation of unnecessary thrombi that might be due to the activation of the coagulation cascade or the circulating platelets. Platelets or thrombocytes play an essential role in hemostasis but abnormal platelet function leads to the development of a number of cardiovascular complications, including thrombotic disorders. Under pathological conditions, platelets are associated with the development of different thrombotic disorders, including atherosclerosis, arterial thrombosis and stroke, deep venous thrombosis and pulmonary embolism; therefore, platelets are the target of a number of anti-thrombotic strategies. Flavonoids, a large group of polyphenols ubiquitously expressed in fruits and vegetables that have attracted considerable attention because of their benefits in human health, including the reduction of the risk of cardiovascular disease. Flavonoids have been reported to reduce platelet activity by attenuating agonist-induced GPIIb/IIIa receptor activation, mobilization of intracellular free Ca2+, granule exocytosis, as well as activation of different signaling molecules such as mitogen- activated protein kinases or phospholipases. This review summarizes the current studies concerning the modulation of platelet activation by flavonoids, giving especial attention to those events associated to thrombotic disorders.

Ageing, Cellular Senescence and Neurodegenerative Disease

Ageing is a major risk factor for developing many neurodegenerative diseases. Cellular senescence is a homeostatic biological process that has a key role in driving ageing. There is evidence that senescent cells accumulate in the nervous system with ageing and neurodegenerative disease and may predispose a person to the appearance of a neurodegenerative condition or may aggravate its course. Research into senescence has long been hindered by its variable and cell-type specific features and the lack of a universal marker to unequivocally detect senescent cells. Recent advances in senescence markers and genetically modified animal models have boosted our knowledge on the role of cellular senescence in ageing and age-related disease. The aim now is to fully elucidate its role in neurodegeneration in order to efficiently and safely exploit cellular senescence as a therapeutic target. Here, we review evidence of cellular senescence in neurons and glial cells and we discuss its putative role in Alzheimer's disease, Parkinson's disease and multiple sclerosis and we provide, for the first time, evidence of senescence in neurons and glia in multiple sclerosis, using the novel GL13 lipofuscin stain as a marker of cellular senescence.

Senescence and senotherapeutics: a new field in cancer therapy

Cellular senescence is a stress response mechanism ensuring homeostasis. Its temporal activation during embryonic development or normal adult life is linked with beneficial properties. In contrast, persistent (chronic) senescence seems to exert detrimental effects fostering aging and age-related disorders, such as cancer. Due to the lack of a reliable marker able to detect senescence in vivo, its precise impact in age-related diseases is to a large extent still undetermined. A novel reagent termed GL13 (SenTraGor^TM) that we developed, allowing senescence recognition in any type of biological material, emerges as a powerful tool to study the phenomenon of senescence in vivo. Exploiting the advantages of this novel methodological approach, scientists will be able to detect and connect senescence with aggressive behavior in human malignancies, such as tolerance to chemotherapy in classical Hodgkin Lymphoma and Langerhans Cell Histiocytosis. The latter depicts the importance of developing the new and rapidly expanding field of senotherapeutic agents targeting and driving to cell death senescent cells. We discuss in detail the current progress of this exciting area of senotherapeutics and suggest its future perspectives and applications.

Impact of specific functional groups in flavonoids on the modulation of platelet activation

Flavonoids exert innumerable beneficial effects on cardiovascular health including the reduction of platelet activation, and thereby, thrombosis. Hence, flavonoids are deemed to be a molecular template for the design of novel therapeutic agents for various diseases including thrombotic conditions. However, the structure-activity relationships of flavonoids with platelets is not fully understood. Therefore, this study aims to advance the current knowledge on structure-activity relationships of flavonoids through a systematic analysis of structurally-related flavones. Here, we investigated a panel of 16 synthetic flavones containing hydroxy or methoxy groups at C-7,8 positions on the A-ring, with a phenyl group or its bioisosteres as the B-ring, along with their thio analogues possessing a sulfur molecule at the 4th carbon position of the C-ring. The antiplatelet efficacies of these compounds were analysed using human isolated platelets upon activation with cross-linked collagen-related peptide by optical aggregometry. The results demonstrate that the hydroxyl groups in flavonoids are important for optimum platelet inhibitory activities. In addition, the 4-C=O and B ring phenyl groups are less critical for the antiplatelet activity of these flavonoids. This structure-activity relationship of flavonoids with the modulation of platelet function may guide the design, optimisation and development of flavonoid scaffolds as antiplatelet agents.

Effect of Polyphenols From Campomanesia adamantium on Platelet Aggregation and Inhibition of Cyclooxygenases: Molecular Docking and in Vitro Analysis

Campomanesia adamantium is a medicinal plant of the Brazilian Cerrado. Different parts of its fruits are used in popular medicine to treat gastrointestinal disorders, rheumatism, urinary tract infections and inflammations. Despite its widespread use by the local population, the mechanisms involving platelet aggregation and the inhibition of cyclooxygenase by C. adamantium are unknown. This study evaluated the chemical composition, antioxidant activities and potential benefits of the C. adamantium peel extract (CAPE) and its components in the platelet aggregation induced by arachidonic acid in platelet-rich plasma. Aspects of the pharmacological mechanism were investigated as follows: platelet viability, calcium mobilization, levels of the cyclic nucleotides cAMP and cGMP, thromboxane B₂ levels, and the inhibitory effects on COX-1 and COX-2 were studied in vitro and using molecular docking in the catalytic domain of these proteins. The major CAPE constituents standing out from the chemical analysis are the flavonoids, namely those of the flavones and chalcones class. The results showed that CAPE, quercetin and myricetin significantly decreased arachidonic acid-induced platelet aggregation; the assays showed that CAPE and quercetin decreased the mobilization of calcium and thromboxane B₂ levels in platelets and increased cAMP and cGMP levels. Moreover, CAPE inhibited the activity of COX-1 and COX-2, highlighting that quercetin could potentially prevent the access of arachidonic acid more to the catalytic site of COX-1 than COX-2. These results highlight CAPE’s potential as a promising therapeutic candidate for the prevention and treatment of diseases associated with platelet aggregation.

Anti-Atherogenic Activity of Polyphenol-Rich Extract from Bee Pollen

The aim of this study was to determine the effect of polyphenol-rich ethanol extract of bee pollen (EEP) on atherosclerosis induced by a high-fat diet in ApoE-knockout mice. EEP was given with feed in two doses of 0.1 and 1 g/kg body mass (BM). The studies have been conducted in a period of 16 weeks. The following factors were estimated: total cholesterol (TC), oxidized low density lipoproteins (ox-LDL), asymmetric dimethylarginine (ADMA), angiotensin-converting enzyme (ACE) and angiotensin II (ANG II) in the 5th, 10th, 12th, 14th, and 16th week of the experiment. In the last, i.e., 16th week of the studies the development of coronary artery disease (CAD) was also estimated histopathologically. Supplementing diet with EEP resulted in decreasing TC level. EEP reduced oxidative stress by lowering the levels of ox-LDL, ADMA, ANG II and ACE. EEP protected coronary arteries by significantly limiting the development of atherosclerosis (the dose of 0.1 g/kg BM) or completely preventing its occurrence (the dose of 1 g/kg BM). The obtained results demonstrate that EEP may be useful as a potential anti-atherogenic agent.

Plant-based Food Cyanidin-3-Glucoside Modulates Human Platelet Glycoprotein VI Signaling and Inhibits Platelet Activation and Thrombus Formation

Background: Platelets play an important role in hemostasis, thrombosis, and atherosclerosis. Glycoprotein VI (GPVI) is a major platelet receptor that interacts with exposed collagen on injured vessel walls. Our previous studies have shown that anthocyanins (a type of natural plant pigment) attenuate platelet function; however, whether anthocyanins affect collagen-induced GPVI signaling remains unknown.Objective: The objective of this study was to explore the effects of cyanidin-3-glucoside (Cy-3-g, one of the major bioactive compounds in anthocyanins) on platelet activation and thrombosis and the GPVI signaling pathway.Methods: Platelets from healthy men and women were isolated and incubated with different concentrations (0, 0.5, 5, and 50 μM) of Cy-3-g. The expression of activated integrin αIIbβ3, P-selectin, CD63, and CD40L, fibrinogen binding to platelets, and platelet aggregation were evaluated in vitro. Platelet adhesion and aggregation in whole blood under flow conditions were assessed in collagen-coated perfusion chambers. Thrombosis and hemostasis were assessed in 3-4-wk-old male C57BL/6J mice through FeCl₃-induced intravital microscopy and tail bleeding time. The effect of Cy-3-g on collagen-induced human platelet GPVI signaling was explored with Western blot.Results: Cy-3-g attenuated platelet function in a dose-dependent manner. The 0.5-μM dose of Cy-3-g inhibited (P < 0.05) human platelet adhesion and aggregation to collagen at both venous (-54.02%) and arterial (-22.90%) shear stresses. The 5-μM dose inhibited (P < 0.05) collagen-induced human platelet activation (PAC-1: -48.21%, P-selectin: -50.63%), secretion (CD63: -73.89%, CD40L: -43.70%), fibrinogen binding (-56.79%), and aggregation (-17.81%). The 5-μM dose attenuated (P < 0.01) thrombus growth (-66.67%) without prolonging bleeding time in mice. The 50-μM dose downregulated (P < 0.05) collagen-induced GPVI signaling in human platelets and significantly decreased phosphorylation of Syk-linker for activation of T cells (LAT)-SLP76 (Syk: -39.08%, LAT: -32.25%, SLP76: -40.00%) and the expression of Lyn (-31.89%), Fyn (-36.27%), and phospholipase C-γ2 (-39.08%).Conclusions: Cy-3-g inhibits human platelet activation, aggregation, secretion, and thrombus formation, and downregulates the collagen-GPVI signaling pathway. Supplementation of Cy-3-g may have protective effects against atherothrombosis.

Effects of quercetin supplementation on lipid profile: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

In spite of promising experimental findings, randomized controlled trials (RCTs) have yielded mixed results on the impact of quercetin supplementation on plasma lipid levels.

AIM

The present study aimed to quantify the effects of quercetin on plasma lipids using a meta-analysis of RCTs.

METHODS

A systematic literature search of Medline was conducted for RCTs that investigated the efficacy of quercetin supplementation on plasma lipids comprising total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated for net changes in lipid concentrations using a random-effects model. Meta-regression analysis was conducted to assess the effect of quercetin dose and duration of supplementation as moderators on the calculated effect measures.

RESULTS

Five RCTs totaling 442 subjects (221 in the quercetin and 221 in the control group) fulfilled the eligibility criteria and selected for analyses. Combined estimate of effect size for the impact of quercetin on plasma LDL-C (WMD: 1.43 mg/dL, 95% CI: -0.92-3.78, p = 0.23), HDL-C (WMD: 0.26 mg/dL, 95% CI: -0.74-1.25, p = 0.61) and triglycerides (WMD: -9.42 mg/dL, 95% CI: -27.80-8.96, p = 0.32) was not statistically significant. However, a borderline significant but clinically non-relevant increase in total cholesterol was observed (WMD: 3.13 mg/dL, 95% CI: -0.01-6.27, p = 0.05). When the analysis was confined to the subgroups of studies with quercetin doses ≥500 mg/day and follow-up of ≥ 4 weeks, a significant increase in total cholesterol (WMD: 3.57 mg/dL, 95% CI: 0.21-6.92, p = 0.04) and a decline in triglycerides (WMD: -24.54 mg/dL, 95% CI: -33.09 to -15.99, p < 0.00001) was observed, but LDL-C and HDL-C concentrations remained unchanged (p > 0.05). Changes in plasma triglycerides, but not other indices of lipid profile, were significantly associated with quercetin dose (slope: -0.057; 95% CI: -0.103 to -0.010; p = 0.02) and duration of supplementation (slope: -5.314; 95% CI: -9.482 to -1.147; p = 0.01).

CONCLUSION

Available evidence from RCTs does not suggest any clinically relevant effect of quercetin supplementation on plasma lipids, apart from a significant reduction of triglycerides at doses above 50 mg/day.

Role of flavonoids and nitrates in cardiovascular health

CVD remain the leading cause of death globally. Effective dietary strategies for their reduction are of high priority. Increasing evidence suggests that phytochemicals, particularly dietary flavonoids and nitrates, are key modulators of CVD risk reduction through impact on multiple risk factors. The aim of this review is to explore the evidence for the impact of flavonoid- and nitrate-rich foods and supplements on CVD risk, with specific reference to their importance as mediators of vascular health and platelet function. There is accumulating evidence to support benefits of dietary flavonoids on cardiovascular health. Dose-dependent recovery of endothelial function and lowering of blood pressure have been reported for the flavanol (-)-epicatechin, found in cocoa, apples and tea, through production and availability of endothelial nitric oxide (NO). Furthermore, flavonoids, including quercetin and its metabolites, reduce in vitro and ex vivo platelet function via inhibition of phosphorylation-dependent cellular signalling pathways, although further in vivo studies are required to substantiate these mechanistic effects. Hypotensive effects of dietary nitrates have been consistently reported in healthy subjects in acute and chronic settings, although there is less evidence for these effects in patient groups. Proposed mechanisms of actions include endothelial-independent NO availability, which is dependent on the entro-salivary circulation and microbial conversion of dietary nitrate to nitrite in the mouth. In conclusion, flavonoid- and nitrate-rich foods show promising effects on vascular function, yet further randomly controlled studies are required to confirm these findings and to determine effective doses.

Relationships Between Bioactive Compound Content and the Antiplatelet and Antioxidant Activities of Six Allium Vegetable Species

Allium sp. vegetables are widely consumed for their characteristic flavour. Additionally, their consumption may provide protection against cardiovascular disease due to their antiplatelet and antioxidant activities. Although antiplatelet and antioxidant activities in Allium sp. are generally recognised, comparative studies of antiplatelet and antioxidant potency among the main Allium vegetable species are lacking. Also, the relationship between organosulfur and phenolic compounds and these biological activities has not been well established. In this study, the in vitro antiplatelet and antioxidant activities of the most widely consumed Allium species are characterised and compared. The species total organosulfur and phenolic content, and the HPLC profiles of 11 phenolic compounds were characterised and used to investigate the relationship between these compounds and antiplatelet and antioxidant activities. Furthermore, antiplatelet activities in chives and shallot have been characterised for the first time. Our results revealed that the strongest antiplatelet agents were garlic and shallot, whereas chives had the highest antioxidant activity. Leek and bunching onion had the weakest both biological activities. Significantly positive correlations were found between the in vitro antiplatelet activity and total organosulfur (R=0.74) and phenolic (TP) content (R=0.73), as well as between the antioxidant activity and TP (R=0.91) and total organosulfur content (R=0.67). Six individual phenolic compounds were associated with the antioxidant activity, with catechin, epigallocatechin and epicatechin gallate having the strongest correlation values (R>0.80). Overall, our results suggest that both organosulfur and phenolic compounds contribute similarly to Allium antiplatelet activity, whereas phenolics, as a whole, are largely responsible for antioxidant activity, with broad variation observed among the contributions of individual phenolic compounds.

Modulation of platelet functions by crude rice (Oryza sativa) bran policosanol extract

Background

Rice bran is bioactive-rich and has proven health benefits for humans. Moreover, its source, the brown rice has antioxidant, hypolipidemic and other functional properties that are increasingly making it a nutritional staple especially in Asian countries. This study investigated the antiplatelet aggregation mechanisms of crude hexane/methanolic rice bran extract, in which policosanol was the targeted bioactive. Platelets play a vital role in pathogenesis of atherosclerosis and cardiovascular diseases, and their increased activities could potentially cause arterial thrombus formation or severe bleeding disorders. Thus, in this study, platelet aggregation and adhesion of platelets to major components of basal lamina were examined in vitro. In addition, cellular protein secretion was quantified as a measurement of platelet activation.

Methods

Adenosine diphosphate (ADP), collagen, and arachidonic acid (AA)-induced aggregation were studied using the microtiter technique. Rat platelets were pre-treated with various concentrations of policosanol extract, and the adhesion of platelets onto collagen- and laminin-coated surface (extracellular matrix) was studied using the acid phosphatase assay. The effect of crude policosanol extract on released proteins from activated platelets was measured using modified Lowry determination method.

Results

Rice bran policosanol extract significantly inhibited in vitro platelet aggregation induced by different agonists in a dose dependent manner. The IC₅₀ of ADP-, collagen-, and AA-induced platelet aggregation were 533.37 ± 112.16, 635.94 ± 78.45 and 693.86 ± 70.57 μg/mL, respectively. The present study showed that crude rice bran policosanol extract significantly inhibited platelet adhesion to collagen in a dose dependent manner. Conversely, at a low concentration of 15.625 μg/mL, the extract significantly inhibited platelet adhesion to laminin stimulated by different platelet agonists. In addition to the alteration of cell adhesive properties, cellular protein secretion of the treated platelets towards different stimulants were decreased upon crude extract treatment.

Conclusion

Our results showed that crude rice bran policosanol extract could inhibit in vitro platelet adhesion, aggregation and secretion upon activation using agonists. These findings serve as a scientific platform to further explore alternative therapies in cardiovascular diseases related to platelet malfunction.

Effects of Quercetin on Blood Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Quercetin, the most abundant dietary flavonol, has antioxidant effects in cardiovascular disease, but the evidence regarding its effects on blood pressure (BP) has not been conclusive. We assessed the impact of quercetin on BP through a systematic review and meta-analysis of available randomized controlled trials.

METHODS AND RESULTS

We searched PUBMED, Cochrane Library, Scopus, and EMBASE up to January 31, 2015 to identify placebo-controlled randomized controlled trials investigating the effect of quercetin on BP. Meta-analysis was performed using either a fixed-effects or random-effect model according to I(2) statistic. Effect size was expressed as weighted mean difference (WMD) and 95% CI. Overall, the impact of quercetin on BP was reported in 7 trials comprising 9 treatment arms (587 patients). The results of the meta-analysis showed significant reductions both in systolic BP (WMD: -3.04 mm Hg, 95% CI: -5.75, -0.33, P=0.028) and diastolic BP (WMD: -2.63 mm Hg, 95% CI: -3.26, -2.01, P<0.001) following supplementation with quercetin. When the studies were categorized according to the quercetin dose, there was a significant systolic BP and diastolic BP-reducing effect in randomized controlled trials with doses ≥500 mg/day (WMD: -4.45 mm Hg, 95% CI: -7.70, -1.21, P=0.007 and -2.98 mm Hg, 95% CI: -3.64, -2.31, P<0.001, respectively), and lack of a significant effect for doses <500 mg/day (WMD: -1.59 mm Hg, 95% CI: -4.44, 1.25, P=0.273 and -0.24 mm Hg, 95% CI: -2.00, 1.52, P=0.788, respectively), but indirect comparison tests failed to significant differences between doses.

CONCLUSIONS

The results of the meta-analysis showed a statistically significant effect of quercetin supplementation in the reduction of BP, possibly limited to, or greater with dosages of >500 mg/day. Further studies are necessary to investigate the clinical relevance of these results and the possibility of quercetin application as an add-on to antihypertensive therapy.

Pharmacological actions of nobiletin in the modulation of platelet function

Background and Purpose

The discovery that flavonoids are capable of inhibiting platelet function has led to their investigation as potential antithrombotic agents. However, despite the range of studies on the antiplatelet properties of flavonoids, little is known about the mechanisms by which flavonoids inhibit platelet function. In this study, we aimed to explore the pharmacological effects of a polymethoxy flavonoid, nobiletin, in the modulation of platelet function.

Experimental Approach

The ability of nobiletin to modulate platelet function was explored by using a range of in vitro and in vivo experimental approaches. Aggregation, dense granule secretion and spreading assays were performed using washed platelets. Fibrinogen binding, α-granule secretion and calcium mobilization assays were performed using platelet-rich plasma and whole blood was used in impedance aggregometry and thrombus formation experiments. The effect of nobiletin in vivo was assessed by measuring tail bleeding time using C57BL/6 mice.

Key Results

Nobiletin was shown to suppress a range of well-established activatory mechanisms, including platelet aggregation, granule secretion, integrin modulation, calcium mobilization and thrombus formation. Nobiletin extended bleeding time in mice and reduced the phosphorylation of PKB (Akt) and PLCγ2 within the collagen receptor (glycoprotein VI)-stimulated pathway, in addition to increasing the levels of cGMP and phosphorylation of vasodilator-stimulated phosphoprotein, a protein whose activity is associated with inhibitory cyclic nucleotide signalling.

Conclusions and Implications

This study provides insight into the underlying molecular mechanisms through which nobiletin modulates haemostasis and thrombus formation. Therefore, nobiletin may represent a potential antithrombotic agent of dietary origins.

Pentamethylquercetin (PMQ) reduces thrombus formation by inhibiting platelet function

Flavonoids exert both anti-oxidant and anti-platelet activities in vitro and in vivo. Pentamethylquercetin (PMQ), a polymethoxylated flavone derivative, has been screened for anti-carcinogenic and cardioprotective effects. However, it is unclear whether PMQ has anti-thrombotic effects. In the present study, PMQ (20 mg/kg) significantly inhibited thrombus formation in the collagen- epinephrine- induced acute pulmonary thrombosis mouse model and the ferric chloride-induced carotid injury model. To explore the mechanism, we evaluated the effects of PMQ on platelet function. We found that PMQ inhibited platelet aggregation and granule secretion induced by low dose agonists, including ADP, collagen, thrombin and U46619. Biochemical analysis revealed that PMQ inhibited collagen-, thrombin- and U46619-induced activation of Syk, PLCγ2, Akt, GSK3β and Erk1/2. Therefore, we provide the first report to show that PMQ possesses anti-thrombotic activity in vivo and inhibited platelet function in vitro, suggesting that PMQ may represent a potential therapeutic candidate for the prevention or treatment of thrombotic disorders.

GRID and docking analyses reveal a molecular basis for flavonoid inhibition of Src family kinase activity

Flavonoids reduce cardiovascular disease risk through anti-inflammatory, anti-coagulant and anti-platelet actions. One key flavonoid inhibitory mechanism is blocking kinase activity that drives these processes. Flavonoids attenuate activities of kinases including phosphoinositide-3-kinase, Fyn, Lyn, Src, Syk, PKC, PIM1/2, ERK, JNK and PKA. X-ray crystallographic analyses of kinase-flavonoid complexes show that flavonoid ring systems and their hydroxyl substitutions are important structural features for their binding to kinases. A clearer understanding of structural interactions of flavonoids with kinases is necessary to allow construction of more potent and selective counterparts. We examined flavonoid (quercetin, apigenin and catechin) interactions with Src family kinases (Lyn, Fyn and Hck) applying the Sybyl docking algorithm and GRID. A homology model (Lyn) was used in our analyses to demonstrate that high-quality predicted kinase structures are suitable for flavonoid computational studies. Our docking results revealed potential hydrogen bond contacts between flavonoid hydroxyls and kinase catalytic site residues. Identification of plausible contacts indicated that quercetin formed the most energetically stable interactions, apigenin lacked hydroxyl groups necessary for important contacts and the non-planar structure of catechin could not support predicted hydrogen bonding patterns. GRID analysis using a hydroxyl functional group supported docking results. Based on these findings, we predicted that quercetin would inhibit activities of Src family kinases with greater potency than apigenin and catechin. We validated this prediction using in vitro kinase assays. We conclude that our study can be used as a basis to construct virtual flavonoid interaction libraries to guide drug discovery using these compounds as molecular templates.

Unconventional approaches to the prevention of cancer associated thrombosis

A number of strategies are currently under investigation to prevent venous thromboembolic events in cancer cohorts. Based on the efficacy of low molecular weight heparin in the treatment of thrombosis in cancer patients, a number of clinical studies have focused on evaluating the efficacy the low molecular weight heparins in the primary thromboprophylaxis setting. Further refinements in defining which cancer cohorts are at greatest risk of suffering thromboembolic events are under investigation such as clinical-laboratory risk scores and biomarkers such as tissue factor-bearing microparticles. However, alternative approaches to primary thromboprophylaxis beyond standard anticoagulants are also being evaluated in the clinic such anti-platelet agents, statins to reduce circulating tissue factor, and scheduled monitoring for venous thromboembolic events without pharmacologic thromboprophylaxis. In addition, clinical studies are underway to evaluate the antithrombotic efficacy of targeting extracellular protein disulfide isomerase with oral flavonoids (e.g. quercetin and isoquercetin). Emerging data regarding these unconventional approaches in the prevention of thromboembolic events in cancer patients is reviewed.

Onion (Allium cepa L.) peel extract has anti-platelet effects in rat platelets

The effects of onion peel extract (OPE) in collagen (5 μg/mL)-stimulated washed rat platelet aggregation were investigated. OPE inhibited platelet aggregation via inhibition of aggregation-inducing molecules, intracellular Ca(2+) and thromboxane A2 (TXA2) by blocking cyclooxygenase-1 (COX-1) and TXA2 synthase (TXAS) activities in a dose-dependent manner. In addition, OPE elevated the formation of cyclic adenosine monophosphate (cAMP), aggregation-inhibiting molecule, but not cyclic guanosine monophosphate (cGMP). High performance liquid chromatography (HPLC) analysis of OPE revealed that OPE contains quercetin, one of the major flavonoids, which has anti-platelet effect. In conclusion, we suggest that OPE is an effective inhibitor of collagen-stimulated platelet aggregation in vitro. Therefore, it can be a promising and safe strategy for anti-cardiovascular diseases.

Investigating flavonoids as molecular templates for the design of small-molecule inhibitors of cell signaling

Epidemiological and clinical trials reveal compelling evidence for the ability of dietary flavonoids to lower cardiovascular disease risk. The mechanisms of action of these polyphenolic compounds are diverse, and of particular interest is their ability to function as protein and lipid kinase inhibitors. We have previously described structure-activity studies that reinforce the possibility for using flavonoid structures as templates for drug design. In the present study, we aim to begin constructing rational screening strategies for exploiting these compounds as templates for the design of clinically relevant, antiplatelet agents. We used the platelet as a model system to dissect the structural influence of flavonoids, stilbenes, anthocyanidins, and phenolic acids on inhibition of cell signaling and function. Functional groups identified as relevant for potent inhibition of platelet function included at least 2 benzene rings, a hydroxylated B ring, a planar C ring, a C ring ketone group, and a C-2 positioned B ring. Hydroxylation of the B ring with either a catechol group or a single C-4' hydroxyl may be required for efficient inhibition of collagen-stimulated tyrosine phosphorylated proteins of 125 to 130 kDa, but may not be necessary for that of phosphotyrosine proteins at approximately 29 kDa. The removal of the C ring C-3 hydroxyl together with a hydroxylated B ring (apigenin) may confer selectivity for 37 to 38 kDa phosphotyrosine proteins. We conclude that this study may form the basis for construction of maps of flavonoid inhibitory activity on kinase targets that may allow a multitargeted therapeutic approach with analogue counterparts and parent compounds.

Tangeretin regulates platelet function through inhibition of phosphoinositide 3-kinase and cyclic nucleotide signaling

OBJECTIVE

Dietary flavonoids have long been appreciated in reducing cardiovascular disease risk factors, but their mechanisms of action are complex in nature. In this study, the effects of tangeretin, a dietary flavonoid, were explored on platelet function, signaling, and hemostasis.

APPROACH AND RESULTS

Tangeretin inhibited agonist-induced human platelet activation in a concentration-dependent manner. It inhibited agonist-induced integrin αIIbβ3 inside-out and outside-in signaling, intracellular calcium mobilization, and granule secretion. Tangeretin also inhibited human platelet adhesion and subsequent thrombus formation on collagen-coated surfaces under arterial flow conditions in vitro and reduced hemostasis in mice. Further characterization to explore the mechanism by which tangeretin inhibits platelet function revealed distinctive effects of platelet signaling. Tangeretin was found to inhibit phosphoinositide 3-kinase-mediated signaling and increase cGMP levels in platelets, although phosphodiesterase activity was unaffected. Consistent with increased cGMP levels, tangeretin increased the phosphorylation of vasodilator-stimulated phosphoprotein at S239.

CONCLUSIONS

This study provides support for the ability and mechanisms of action of dietary flavonoids to modulate platelet signaling and function, which may affect the risk of thrombotic disease.

Ethyl acetate extract from tissue-cultured mountain ginseng adventitious roots inhibits in vitro platelet aggregation in whole human blood and augments peripheral blood flow in mice

We previously reported that in vitro anti-platelet activity of tissue-cultured mountain ginseng (TCMG) ethanol extracts show improved efficacy when compared with commercial ginseng products such as Korean red ginseng and Panax ginseng. However, information on the anti-platelet activity of the ethyl acetate fraction from TCMG adventitious roots is limited. Therefore, in this study, we further investigated the effects of an ethyl acetate extract of TCMG (EA-TCMG) adventitious roots on in vitro antiplatelet activity in whole human blood and its effect on peripheral blood flow in mice. We found that EA-TCMG inhibited platelet aggregation with IC₅₀ values of 271, 180, and 147 μg/mL induced by collagen, adenosine-5΄-diphosphate, and arachidonic acid, respectively. Among the three agonists used, thromboxane A₂ formation induced by arachidonic acid was markedly suppressed. Furthermore, EA-TCMG improved the peripheral circulatory disturbance by improving vascular blood flow. In conclusion, these results suggest that ethyl acetate extracts from TCMG adventitious roots might inhibit vascular platelet aggregation and thrombus formation.

Effect of quercetin-rich onion peel extracts on arterial thrombosis in rats

The aim of this study was to examine whether oral supplementation of quercetin-rich onion peel extract (OPE) influences blood coagulation and arterial thrombosis in Sprague-Dawley (SD) rats. 24 male rats, 5 weeks old, were divided into three groups with different diets (C: control, 2mg OPE: chow diet with 2mg OPE supplementation, 10mg OPE: chow diet with 10mg OPE supplementation) for 6 weeks. Blood coagulation parameters including prothrombin time (PT), activated partial thromboplastin time (aPTT) and platelet aggregation were examined. The OPE did not affect blood cholesterol levels but significantly decreased blood triglyceride and glucose levels. PT, aPTT and platelet aggregation were not significantly different among all tested groups. However, in vivo arterial thrombosis was significantly delayed in groups that were fed 2mg and 10mg OPE diets compared to the control group. In addition, the OPE greatly diminished thrombin-induced expression of tissue factor in human umbilical vein endothelial cells (HUVECs), a coagulation initiator. In addition, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways activated by thrombin treatment were prevented by the OPE pre-treatment. These results indicate that OPE may have anti-thrombotic effects through restricting the induced expression of tissue factor via down-regulating mitogen-activated protein kinase (MAPK) activation upon coagulation stimulus, leading to the prolongation of time for arterial thrombosis.

Grape Seed Extracts Inhibit Platelet Aggregation by Inhibiting Protein Tyrosine Phosphatase

Platelets play an important role in various thrombotic diseases, including myocardial infarction. Because red wine consumption is inversely associated with death due to ischemic heart diseases, the effects of grape components on platelet function have been extensively investigated. Grape seed extracts (GSEs) reportedly inhibit platelet aggregation; however, the underlying mechanism has not been elucidated. We discovered that GSEs inhibit platelet aggregation induced by collagen and thrombin-receptor agonist peptide and increase basal levels of tyrosine phosphorylation, which was also observed in the presence of a protein tyrosine phosphatase (PTP) inhibitor. An in vitro phosphatase assay indicated that GSE dose dependently inhibited PTP-1B and Src homology 2 domain-containing phosphatase-1 activity, which positively regulates platelet aggregation. We propose that GSEs inhibit platelet aggregation by inhibiting tyrosine phosphatase activity. Moreover, we showed that GSE ingestion inhibited platelet aggregation in mice without enhancing tail bleeding, implying that GSE supplementation might be beneficial to prevention of thrombotic diseases.

Ginsenoside-Rp1 inhibits platelet activation and thrombus formation via impaired glycoprotein VI signalling pathway, tyrosine phosphorylation and MAPK activation

BACKGROUND AND PURPOSE

Ginsenosides are the main constituents for the pharmacological effects of Panax ginseng. Such effects of ginsenosides including cardioprotective and anti-platelet activities have shown stability and bioavailability limitations. However, information on the anti-platelet activity of ginsenoside-Rp1 (G-Rp1), a stable derivative of ginsenoside-Rg3, is scarce. We examined the ability of G-Rp1 to modulate agonist-induced platelet activation.

EXPERIMENTAL APPROACH

G-Rp1 in vitro and ex vivo effects on agonist-induced platelet-aggregation, granule-secretion, [Ca(2+) ](i) mobilization, integrin-α(IIb) β(3) activation were examined. Vasodilator-stimulated phosphoprotein (VASP) and MAPK expressions and levels of tyrosine phosphorylation of the glycoprotein VI (GPVI) signalling pathway components were also studied. G-Rp1 effects on arteriovenous shunt thrombus formation in rats or tail bleeding time and ex vivo coagulation time in mice were determined. KEY RESULT: G-Rp1 markedly inhibited platelet aggregation induced by collagen, thrombin or ADP. While G-Rp1 elevated cAMP levels, it dose-dependently suppressed collagen-induced ATP-release, thromboxane secretion, p-selectin expression, [Ca(2+) ](i) mobilization and α(IIb) β(3) activation and attenuated p38(MAPK) and ERK2 activation. Furthermore, G-Rp1 inhibited tyrosine phosphorylation of multiple components (Fyn, Lyn, Syk, LAT, PI3K and PLCγ2) of the GPVI signalling pathway. G-Rp1 inhibited in vivo thrombus formation and ex vivo platelet aggregation and ATP secretion without affecting tail bleeding time and coagulation time, respectively.

CONCLUSION AND IMPLICATIONS

G-Rp1 inhibits collagen-induced platelet activation and thrombus formation through modulation of early GPVI signalling events, and this effect involves VASP stimulation, and ERK2 and p38(-MAPK) inhibition. These data suggest that G-Rp1 may have therapeutic potential for the treatment of cardiovascular diseases involving aberrant platelet activation.

Insights into dietary flavonoids as molecular templates for the design of anti-platelet drugs

Flavonoids are low-molecular weight, aromatic compounds derived from fruits, vegetables, and other plant components. The consumption of these phytochemicals has been reported to be associated with reduced cardiovascular disease (CVD) risk, attributed to their anti-inflammatory, anti-proliferative, and anti-thrombotic actions. Flavonoids exert these effects by a number of mechanisms which include attenuation of kinase activity mediated at the cell-receptor level and/or within cells, and are characterized as broad-spectrum kinase inhibitors. Therefore, flavonoid therapy for CVD is potentially complex; the use of these compounds as molecular templates for the design of selective and potent small-molecule inhibitors may be a simpler approach to treat this condition. Flavonoids as templates for drug design are, however, poorly exploited despite the development of analogues based on the flavonol, isoflavonone, and isoflavanone subgroups. Further exploitation of this family of compounds is warranted due to a structural diversity that presents great scope for creating novel kinase inhibitors. The use of computational methodologies to define the flavonoid pharmacophore together with biological investigations of their effects on kinase activity, in appropriate cellular systems, is the current approach to characterize key structural features that will inform drug design. This focussed review highlights the potential of flavonoids to guide the design of clinically safer, more selective, and potent small-molecule inhibitors of cell signalling, applicable to anti-platelet therapy.

Inhibition of platelet-mediated arterial thrombosis and platelet granule exocytosis by 3',4'-dihydroxyflavonol and quercetin

Flavonols are polyphenolic compounds with broad-spectrum kinase inhibitory, as well as potent anti-oxidant and anti-inflammatory properties. Anti-platelet potential of quercetin (Que) and several related flavonoids have been reported; however, few studies have assessed the ability of flavonols to inhibit exocytosis of different platelet granules or to inhibit thrombus formation in vivo. 3',4'-Dihydroxyflavonol (DiOHF) is a flavonol which is structurally related to Que and has been shown to have greater anti-oxidant capacity and to improve the endothelial function in the context of diabetes and ischaemia/reperfusion injury. While the structural similarity to Que suggests DiOHF may have a potential to inhibit platelet function, no studies have assessed the anti-platelet potential of DiOHF. We therefore investigated platelet granule inhibition and potential to delay arterial thrombosis by Que and DiOHF. Both Que and DiOHF showed inhibition of collagen, adenosine diphosphate and arachidonic acid stimulated platelet aggregation, agonist-induced GPIIb/IIIa activation as demonstrated by PAC-1 and fibrinogen binding. While both flavonols inhibited agonist-induced granule exocytosis, greater inhibition of dense granule exocytosis occurred with DiOHF as measured by both ATP release and flow cytometry. In contrast, while Que inhibited agonist-induced P-selectin expression, as measured by both platelet surface P-selectin expression and upregulation of surface GPIIIa expression, inhibition by DiOHF was not significant for either parameter. C57BL/6 mice treated with 6 mg kg(-1) IV Que or DiOHF maintained greater blood flow following FeCl3-induced carotid artery injury when compared to the vehicle control. We provide evidence that Que and DiOHF improve blood flow following arterial injury in part by attenuating platelet granule exocytosis.