Flavone-8-acetic acid (Flavonoid) profoundly reduces platelet-dependent thrombosis and vasoconstriction after deep arterial injury In vivo

Quercitrin inhibits platelet activation in arterial thrombosis

BACKGROUND

The ingestion of flavonoids has been reported to be associated with reduced cardiovascular disease risk. Quercitrin is a common flavonoid in nature, and it exhibits antioxidant properties. Although the process of thrombogenesis is intimately related to cardiovascular disease risk, it is unclear whether quercitrin plays a role in thrombogenesis.

PURPOSE

The aim of this study was to examine the antiplatelet effect of quercitrin in platelet activation.

METHODS

Platelet aggregation, granule secretion, calcium mobilization, and integrin activation were used to assess the antiplatelet activity of quercitrin. Antithrombotic effect was determined in mouse using ferric chloride (FeCl3)-induced arterial thrombus formation in vivo and thrombus formation on collagen-coated surfaces under arteriolar shear in vitro. Transection tail bleeding time was used to evaluate whether quercitrin inhibited primary hemostasis.

RESULTS

Quercitrin significantly impaired collagen-related peptide-induced platelet aggregation, granule secretion, reactive oxygen species generation, and intracellular calcium mobilization. Outside-in signaling of αIIbβ3 integrin was significantly inhibited by quercitrin in a concentration-dependent manner. The inhibitory effect of quercitrin resulted from inhibition of the glycoprotein VI-mediated platelet signal transduction during cell activation. Further, the antioxidant effect is derived from decreased phosphorylation of components of the TNF receptor-associated factor 4/p47phox/Hic5 axis signalosome. Oral administration of quercitrin efficiently blocked FeCl3-induced arterial thrombus formation in vivo and thrombus formation on collagen-coated surfaces under arteriolar shear in vitro, without prolonging bleeding time. Studies using a mouse model of ischemia/reperfusion-induced stroke indicated that treatment with quercitrin reduced the infarct volume in stroke.

CONCLUSIONS

Our results demonstrated that quercitrin could be an effective therapeutic agent for the treatment of thrombotic diseases.

Anticoagulant effect and safety assessment of an aqueous extract of Pseudocedrela kotschyi (Schweinf.) harms and Adenia cissampeloides (Planch. Ex Hook.) harms

BACKGROUND

Currently available therapeutic options for thromboembolic disorders are often very expensive and are associated with unfavorable side effects.

AIM

To establish the anticoagulant effect and safety profile of an extract made from of the root bark of Pseudocedrela kotschyi (Schweinf.) Harms and the aerial part of Adenia cissampeloides (Planch. ex Hook.) Harms (PAE).

MATERIALS AND METHODS

PAE (0.5-2.0 g/L) effect on prothrombin time (PT) and activated partial thromboplastin time (aPTT) were evaluated on whole blood drawn from the marginal ear vein of New Zealand White rabbits. Effect of PAE (250-2000 mg/kg) on bleeding time (BT) and clotting time (CT) in Sprague-Dawley rats were also assessed. Histopathological, hematological, and liver function studies were also carried out to assess the safety for use of PAE (250-2000 mg/kg).

RESULTS

PAE had no significant effect (P > 0.05) on PT, but resulted in a significant increase (P ≤ 0.05-0.0001) in aPTT. The PAE treatment resulted in a significant increase (P ≤ 0.05-0.0001) in BT and CT in vivo compared with control. Safety studies indicated no deaths with PAE treatment with hematological and liver function tests being normal. Histological studies revealed pathological changes in the liver at a PAE treatment dose of 2000 mg/kg but all doses had no detrimental effect on kidney and stomach tissue. The no-observed-adverse-effect-level was <2000 mg/kg when given orally.

CONCLUSION

PAE has anticoagulant effect in vitro and is safe to use at oral doses <2000 mg/kg.

Evaluation of the antithrombotic effects of Crataegus monogyna and Crataegus davisii in the carrageenan-induced tail thrombosis model

CONTEXT

Crataegus species are widely used as herbal medicines for preventing cardiovascular diseases (CVDs). However, there are no studies on the effects of Crataegus monogyna Jacq. (Rosaceae) and C. davisii Browicz on thrombosis, which is an important mechanism in CVDs.

OBJECTIVE

The purpose of this study was to investigate the antithrombotic effects of ethanol extracts of Crataegus monogyna (CMEx) and C. davisii (CDEx) leaves by using the carrageenan-induced tail thrombosis model.

MATERIALS AND METHODS

The hind paw of each mouse was injected with 1% Type I carrageenan to induce thrombosis. CMEx was tested at the doses of 100, 200, and 300 mg/kg and CDEx at the dose of 50, 100, 200, and 300 mg/kg in comparison with heparin. The lengths of tail thrombosis were measured at the 24, 48, and 72 h.

RESULTS

Does of 200 and 300 mg/kg CMEx showed significant effects (p < 0.01; p < 0.001) at 24 h when compared with the control group. The antithrombotic activity of 200 and 300 mg/kg CMEx showed a decrease at 48 and 72 h but the activity of 300 mg/kg dose of CMEx was still significant (p < 0.01). The activities of 50 and 100 mg/kg doses of CDEx were significant (p < 0.001; p < 0.01) between 24 and 72 h whereas 200 and 300 mg/kg CDEx did not show any significance.

DISCUSSION AND CONCLUSIONS

CMEx and CDEx significantly inhibited the carrageenan-induced mouse tail thrombosis. Based on these results, it was concluded that CDEx and CMEx may potentially be used as therapeutic agents or complementary treatments against thrombosis.

Tumor vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid inhibits platelet activation and thrombosis via inhibition of thromboxane A2 signaling and phosphodiesterase

BACKGROUND

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is a tumor vascular disrupting agent under clinical trials as an adjacent antitumor agent. DMXAA is structurally similar to flavone-8-acetic acid (FAA), an old tumor vascular disrupting agent with antiplatelet and antithrombotic effects. In contrast to FAA, which causes bleeding in tumor patients, no bleeding has been reported in patients receiving DMXAA. Whether DMXAA also affects platelet function is not clear.

OBJECTIVES

To determine the effects of DMXAA on platelet function and explore the underlying mechanisms.

METHODS AND RESULTS

DMXAA concentration-dependently inhibited human platelet aggregation and ATP release induced by U46619, arachidonic acid, ADP, collagen, or ristocetin. Furthermore, DMXAA inhibited phosphorylation of Erk1/2 and Akt downstream of thromboxane A2 signaling inhibition. DMXAA also inhibited human platelet phosphodiesterase. The antiplatelet effects were further confirmed using mice administered DMXAA intravenously. DMXAA dramatically inhibited thrombus formation in FeCl3 -injured mouse mesenteric arterial thrombus model and laser-injured mouse cremaster arteriole thrombus model. Notably, at a dose exhibiting antithrombotic effects similar to those of clopidogrel in mice, DMXAA did not significantly increase bleeding.

CONCLUSIONS

For the first time, we found that tumor vascular disrupting agent DMXAA has potent antiplatelet and antithrombotic effects without any bleeding diathesis. As DMXAA inhibits platelet activity with safe profile, DMXAA could be used as an efficacious and safe antiplatelet drug.

Antithrombotic effects of ethanol extract of Crataegus orientalis in the carrageenan-induced mice tail thrombosis model

INTRODUCTION

Crataegus species (common name is Hawthorn) are medicinal plants, which have flavonoids, triterpene acids, proanthocyanidins, and organic acids as main constituents, used in the treatment of cardiovascular diseases. One of the main causes of multiple cardiovascular diseases is intravascular thrombosis and current agents, which are used for the treatment and prevention of thrombosis, have some side effects. Therefore, new antithrombotic and thrombolytic agents are still needed.

MATERIALS AND METHODS

Antithrombotic function of ethanol extract of Crataegus orientalis (COE) leaves was investigated in carrageenan-induced mice tail thrombosis model. Mice were injected with 40 μl (1%) carrageenan (Type I) dissolved in physiological saline by intraplantar administration in the right hind paw. After carrageenan injection, the extract was administered at the doses of 100, 200, and 300 mg/kg. Heparin was used as a positive control (10 and 100 IU). The length of tail-thrombosis was measured at 24th, 48th, and 72nd hours.

RESULTS AND CONCLUSION

100mg/kg COE and 10IU heparin were not significant when compared to control groups at the time interval (24-72 h) that results was obtained. At 24th hour, both 200 and 300 mg/kg of COE showed a significant antithrombotic activity (p<0.05 and p<0.01, respectively). However, 200 mg/kg COE lost its significance and there was a decrease in the significance values of 300 mg/kg COE (p<0.05) at 48 and 72 h. From these results, it was concluded that COE significantly inhibited carrageenan-induced mice tail thrombosis in vivo.

The flavonoid luteolin inhibits niacin-induced flush

BACKGROUND AND PURPOSE

Sustained release niacin effectively lowers serum cholesterol, LDL and triglycerides, while raising HDL. However, 75% of patients experience cutaneous warmth and itching known as flush, leading to discontinuation. Acetylsalicylic acid (aspirin) reduces this flush only by about 30%, presumably through decreasing prostaglandin D2 (PGD2). We investigated whether niacin-induced flush in a rat model involves PGD2 and 5-HT, and the effect of certain flavonoids.

EXPERIMENTAL APPROACH

Three skin temperature measurements from each ear were recorded with an infrared pyrometer for each time point immediately before i.p. injection with either niacin or a flavonoid. The temperature was then measured every 10 min for 60 min.

KEY RESULTS

Niacin (7.5 mg per rat, equivalent to a human dose of 1750 mg per 80 kg) maximally increased ear temperature to 1.9+/-0.2 degrees C at 45 min. Quercetin and luteolin (4.3 mg per rat; 1000 mg per human), administered i.p. 45 min prior to niacin, inhibited the niacin effect by 96 and 88%, respectively. Aspirin (1.22 mg per rat; 325 mg per human) inhibited the niacin effect by only 30%. Niacin almost doubled plasma PGD2 and 5-HT, but aspirin reduced only PGD2 by 86%. In contrast, luteolin inhibited both plasma PGD2 and 5-HT levels by 100 and 67%, respectively. CONCLUSIONS AND IMPLICATIONS. Niacin-induced skin temperature increase is associated with PGD2 and 5-HT elevations in rats; luteolin may be a better inhibitor of niacin-induced flush because it blocks the rise in both mediators.

The altered homeostatic theory: A hypothesis proposed to be useful in understanding and preventing ischemic heart disease, hypertension, and diabetes – including reducing the risk of age and atherosclerosis

Evidence will be presented to support the usefulness of the altered homeostatic theory in understanding basic pathogenetic mechanisms of ischemic heart disease (IHD), hypertension, and diabetes, and in improving prevention of these disorders. The theory argues that: IHD, hypertension, and diabetes share the same basic pathogenesis; risk factors favor a sympathetic homeostatic shift; preventative factors favor a parasympathetic homeostatic shift; risk and preventative factors oppose each other through a dynamic risk/prevention balance; and prevention should be based on improving the risk/prevention balance. Prevention based on improving the risk/prevention balance should be more effective, as this method is regarded as reflecting more accurately basic pathogenetic mechanisms. As example, the theory argues that the risk of supposedly nonmodifiable risk factors as age and the risk of relatively nonmodifiable atherosclerosis can be reduced significantly. The possible validity of the altered homeostatic theory was tested by a study based on multiple associations. Findings support a common pathogenesis for IHD, hypertension, and diabetes based on a sympathetic homeostatic shift, and the usefulness of prevention based on improving the risk/prevention balance by using standard pharmaceutical and lifestyle preventative measures. The same set of multiple and diverse risk factors favored IHD, hypertension, and diabetes, and the same set of multiple and diverse pharmaceutical and lifestyle preventative measures prevented these disorders. Also, the same set of preventative agents generally improved cognitive function and bone density, and reduced the incidence of Alzheimer's disease, atrial fibrillation, and cancer. Unexpectedly, evidence was developed that four major attributes of sympathetic activation represent four major risk factors; attributes of sympathetic activation are a tendency toward thrombosis and vasoconstriction, lipidemia, inflammation, and hyperglycemia, and corresponding risk factors are endothelial dysfunction (which expresses thrombosis/vasoconstriction and epitomizes this tendency), dyslipidemia, inflammation, and insulin resistance. These findings, plus other information, provide evidence that dyslipidemia acts mainly as a marker of risk of IHD, rather than being the basic mechanism of this disorder. However, prevention generally is based solely on improvement of dyslipidemia; basing prevention on dyslipidemia relatively underemphasizes the importance of other significant risk factors and, by certifying its validity, discourages alternate pathogenetic approaches. Also, development of myocardial infarction is approached differently. It seems generally accepted that dyslipidemia results rather automatically in infarction through the sequence of atherosclerosis, atherosclerotic complications, and thrombosis. In contrast, distinction is made between development of atherosclerosis and acute induction of infarction--where atherosclerosis is only one of multiple risk factors.

Flavonoid classes and risk of peripheral arterial occlusive disease: a case-control study in Greece

OBJECTIVE

To assess the relation between specific flavonoid classes and peripheral arterial occlusive disease (PAOD), an important manifestation of atherosclerosis.

DESIGN

Using data from a case-control study conducted in Greece in 1980 on the nutritional epidemiology of PAOD, we have exploited recently published databases on the content of foods in specific flavonoid classes to assess the relation between intake of these compounds and PAOD.

SETTING

A major teaching hospital in Athens, Greece.

SUBJECTS

Cases were 100 patients with PAOD and controls 100 patients with minor surgical conditions admitted to the same hospital.

INTERVENTIONS

No interventions. All cases and controls were interviewed in the hospital wards, and a 110-food item semiquantitative food frequency questionnaire was administered by the same interviewer.

RESULTS

Flavonols, flavones and perhaps flavan-3-ols were inversely associated with PAOD risk, the odds ratios (and 95% confidence intervals) for increments equal to the corresponding standard deviations being 0.41 (0.20-0.86), 0.56 (0.32-0.96) and 0.53 (0.26-1.05), respectively. Total flavonoids were also significantly inversely associated with PAOD.

CONCLUSIONS

On the basis of these results, the biological properties of flavonoids and evidence concerning their relation to other manifestations of atherosclerosis, we conclude that dietary intake of specific classes of flavonoids, as well as total flavonoids, may have a protective effect against PAOD.

SPONSORSHIP

This study was partially supported by a grant to Harvard University by the Samourkas Foundation.

Flavonoid-mediated inhibition of actin polymerization in cold-activated platelets

The response of human platelets to low temperature (below 15 degrees C) requires that they are stored at elevated temperatures and limits their storage time to 5 days for use in transfusion. Prolonged storage at room temperature leads to loss of platelet function and risk of septic conditions. The need for improved platelet storage is an important issue, and finding a key component allowing platelets to be maintained at low temperatures would have significant practical benefit. Developing such a component is challenging, because the process of cold-activation resembles that of a physiological agonist-mediated activation, but without a specific receptor that can be inhibited. A component preventing platelets' low temperature response will potentially inhibit their physiological function, making them less useful after transfusion. In the present study, we report that pretreatment of platelets with flavonoids before chilling prevents an increase in cytosolic calcium concentration, actin polymerization and platelet shape change. After warming, platelets that were chilled in the presence of flavonoids retain a normal shape change and aggregation response after stimulation by thrombin. Additionally, cold platelet activation does not increase platelet procoagulant activity evaluated by annexin V-FITC binding in the presence and absence of flavonoids. These data confirm the important links that exist between agonist- and cold-mediated platelet activation, suggesting a possible advantage of incorporating the use of flavonoids to allow platelet hypothermic-storage.

Flavonoids inhibit platelet function through binding to the thromboxane A2 receptor

BACKGROUND

Dietary flavonoids are known for their antiplatelet activity resulting in cardiovascular protection, although the specific mechanisms by which this inhibition occurs has not been fully established.

OBJECTIVE

The aim of this study was to investigate the interaction of nine flavonoids representative of various chemical classes, with platelet responses dependent on thromboxane A(2) (TxA(2)) generation and on receptor antagonism, and to analyze the structural requirements for such effects.

METHODS

The effect of several types of flavonoids on platelet aggregation, serotonin release, and TxA(2) generation was investigated. Competitive radioligand binding assays were used to screen for affinity of these compounds to TxA(2) receptors.

RESULTS

Flavones (apigenin and luteolin) and isoflavones (genistein) abrogated arachidonic acid and collagen-induced platelet responses, such as aggregation and secretion, with a less substantial effect on TxA(2) synthesis. These compounds were identified as specific ligands of the TxA(2) receptor in the micromol L(-1) range, this effect accounting for antiplatelet effects related to stimulation with those agonists. Tight binding of flavonoids to the human TxA(2) receptor relies on structural features such as the presence of the double bond in C2-C3, and a keto group in C4.

CONCLUSIONS

The inhibition by specific flavonoids of in vitro platelet responses induced by collagen or arachidonic acid seems to be related, to a great extent, to their ability to compete for binding to the TxA(2) receptor. Therefore, antagonism of this TxA(2) receptor may represent an additional mechanism for the inhibitory effect of these compounds in platelet function.

Potentiation of antiaggregating effect of prostaglandins by alpha-tocopherol and quercetin

Prostaglandin (PG) I2 (prostacyclin), PGE1 and their analogues are effective inhibitors of platelet aggregation. However, a clinical use of these compounds for the treatment of cardiovascular diseases is restricted due to unwanted side effects. Alpha-tocopherol and quercetin are weak antiplatelet agents. At the same time, they have mild if any side effects when consumed medicinally. The aim of this work was to study the possibility to decrease the effective antiplatelet concentrations of PGs combining them with alpha-tocopherol or quercetin. Platelet-rich plasma (PRP) was prepared from human blood. The inhibition of adenosine diphosphate-induced platelet aggregation was caused by PGs in the presence and absence of alpha-tocopherol or quercetin and corresponding concentration-effect curves were obtained. At a subthreshold concentration 200 and 2 microM, respectively, both alpha-tocopherol and quercetin essentially increased the antiplatelet effects of PGI2, PGE1 and iloprost. Especially effective was the combination of alpha-tocopherol with low concentrations of iloprost. Thus, combination of PGs with alpha-tocopherol or quercetin allows the use of prostaglandins at lower concentrations to inhibit platelet aggregation.

Interaction of the 268-282 region of glycoprotein Ibalpha with the heparin-binding site of thrombin inhibits the enzyme activation of factor VIII

Activation of factor VIII (FVIII) by thrombin plays a fundamental role in the amplification of the coagulation cascade and takes place through specific proteolytic cleavages at Arg(372), Arg(740) and Arg(1689). Full FVIII activation requires cleavage at Arg(372), a process involving the alpha-thrombin exosite-II; referred to as heparin-binding site (HBS). The present study was aimed at investigating the effect of glycoprotein Ibalpha (GpIbalpha; 1-282 fragment) binding to thrombin HBS on FVIII activation. Similar experiments were also performed using a synthetic peptide modelled on the 268-282 sequence of GpIbalpha, and sulphated successfully at all tyrosine residues present along its sequence, at positions 276, 278 and 279. Both GpIbalpha 1-282 and the sulphated GpIb 268-282 peptides induced a progressive decrease (up to 70%) in activated FVIII generation, assessed by coagulation and FXa-generation assays. Furthermore, SDS/PAGE and Western-blot experiments showed that the specific appearance of the 44 kDa A2 domain on cleavage of the FVIII Arg(372)-Ser(373) peptide bond was delayed significantly in the presence of either GpIbalpha 1-282 or GpIb 268-282 peptide. Moreover, the effect of the latter on thrombin-mediated hydrolysis of a peptide having the sequence 341-376 of FVIII was investigated using reverse-phase HPLC. The k (cat)/ K (m) values of the FVIII 341-376 peptide hydrolysis by thrombin decreased linearly as a function of the GpIbalpha 268-282 peptide concentration, according to a competitive inhibition effect. Taken together, these experiments suggest that the sulphated 268-282 region of GpIbalpha binds to thrombin HBS, and is responsible for the inhibition of the Arg(372)-Ser(373) bond cleavage and activation of FVIII.

Genistein, an isoflavone included in soy, inhibits thrombotic vessel occlusion in the mouse femoral artery and in vitro platelet aggregation

Diet can be the most important factor that influences risks for cardiovascular diseases. Genistein included in soy is one candidate that may benefit the cardiovascular system. Here, we investigated the inhibitory effects of genistein on thrombotic vessel occlusion in the mouse femoral artery using a photochemical reaction, and in vitro platelet aggregation in whole blood measured by single platelet counting. Genistein (10 mg/kg), intravenously administered 10 min before the rose bengal injection, significantly prolonged the thrombotic occlusion time from 6.1+/-0.4 to 8.4+/-0.8 min (P<0.05). Genistein at doses higher than 30 microM significantly (P<0.01) inhibited in vitro platelet aggregation induced by collagen (1 and 3 microg/ml). When 10 mg/kg genistein was intravenously administered, ex vivo platelet aggregation induced by collagen (1 and 3 microg/ml) was significantly suppressed (P<0.01). In conclusion, genistein prevented in vivo thrombogenesis and suppressed in vitro platelet aggregation. These results suggest that dietary supplementation of soy may prevent the progression of thrombosis and atherosclerosis.

Novel approaches to the treatment of thrombosis

Thromboembolic diseases remain the main cause of death in Western societies despite current antithrombotic treatments. Recent advances in the molecular bases of haemostasis have highlighted new targets for novel antiplatelet or anticoagulant agents. Considering antiplatelet agents, selective antagonists of specific receptors (von Willebrand factor, collagen or thrombin receptors) are effective in thrombosis models and direct ADP receptor antagonists and nitric-oxide-releasing aspirin are in Phase I-II clinical trials. Concerning anticoagulants, inhibitors of tissue-factor-induced clotting activation, selective inhibitors of thrombin and factor Xa, and components of the anticoagulant protein C system (recombinant activated human protein C or human soluble thrombomodulin) have been studied. Some of these agents have had promising results in Phase III studies. Several achievements are anticipated from the development of new antithrombotics, including a further reduction of cardiovascular mortality and unwanted bleeding, and easier patient management.