Antiplatelet agents for secondary prevention of ischemic stroke

DK-MGAR101, an extract of adventitious roots of mountain ginseng, improves blood circulation by inhibiting endothelial cell injury, platelet aggregation, and thrombus formation

Background

Since ginsenosides exert an anti-thrombotic activity, blood flow-improving effects of DK-MGAR101, an extract of mountain ginseng adventitious roots (MGAR) containing various ginsenosides, were investigated in comparison with an extract of Korean Red Ginseng (ERG).

Methods

In Sprague-Dawley rats orally administered with DK-MGAR101 or ERG, oxidative carotid arterial thrombosis was induced with FeCl₃ (35%), and their blood flow and occlusion time were measured. To elucidate underlying mechanisms, the cytoprotective activities on rat aortic endothelial cells (RAOECs) exposed to hydrogen peroxide (H₂O₂) were confirmed. In addition, the inhibitory activities of DK-MGAR101 and ERG on agonist-induced platelet aggregation, thromboxane B₂ production, and ATP granule release from stimulated platelets as well as blood coagulation were analyzed.

Results

DK-MGAR101 containing high concentrations of Rb1, Rg1, Rg3, Rg5, and Rk1 ginsenosides (55.07 mg/g) was more effective than ERG (ginsenosides 8.45 mg/g) in protecting RAOECs against H₂O₂ cytotoxicity. DK-MGAR101 was superior to ERG not only in suppressing platelet aggregation, thromboxane B₂ production, and granule release, but also in delaying blood coagulation, FeCl₃-induced arterial occlusion, and thrombus formation.

Conclusions

The results indicate that DK-MGAR101 prevents blood vessel occlusion by suppressing platelet aggregation, thrombosis, and blood coagulation, in addition to endothelial cell injury.

Cerebro-renal interaction and stroke

Stroke is an event causing a disturbance in cerebral function leading to death and disability worldwide. Both acute kidney injury and chronic kidney disease (CKD) are associated with an increased risk of stroke and cerebrovascular events. The underlying mechanistic approach between impaired renal function and stroke is limitedly explored and has attracted researchers to learn more for developing therapeutic intervention. Common risk factors such as hypertension, hyperphosphatemia, atrial fibrillation, arteriosclerosis, hyperhomocysteinemia, blood-brain barrier disruption, inflammation, etc. are observed in the general population, but are high in renal failure patients. Also, risk factors like bone mineral metabolism, uremic toxins, and anemia, along with the process of dialysis in CKD patients, eventually increases the risk of stroke. Therefore, early detection of risks associated with stroke in CKD is imperative, which may decrease the mortality associated with it. This review highlights mechanisms by which kidney dysfunction can lead to cerebrovascular events and increase the risk of stroke in renal impairment.

Antiplatelet Activity of Acylphloroglucinol Derivatives Isolated from Dryopteris crassirhizoma

Platelets are an important component of the initial response to vascular endothelial injury; however, platelet dysfunction induces the acute clinical symptoms of thrombotic disorders, which trigger severe cardiovascular diseases such as myocardial infarction, ischemia, and stroke. In this study, we investigated the Dryopteris crassirhizoma's antiplatelet activity. A water extract of D. crassirhizoma (WDC) was partitioned into dichloromethane (DCM), ethyl acetate, n-butyl alcohol, and water. Among these four fractions, the DCM fraction potently inhibited the collagen-stimulated platelet aggregation in a concentration-dependent manner. From this fraction, five different acylphloroglucinol compounds and one flavonoid were isolated by activity-guided column chromatography. They were identified by comparing their mass, ¹H-, and ¹³C-NMR spectral data with those reported in the literature. Quantifying the six compounds in WDC and its DCM fraction by high-performance liquid chromatography (HPLC) revealed that butyryl-3-methylphloroglucinol (compound 4) was the most abundant in these samples. Additionally, butyryl-3-methylphloroglucinol showed the strongest inhibitory activity in the collagen- and arachidonic acid (AA)-induced platelet aggregation, with inhibition ratios of 92.36% and 89.51% in the collagen and AA-induced platelet aggregation, respectively, without cytotoxicity. On the active concentrations, butyryl-3-methylphloroglucinol significantly suppressed the convulxin-induced platelet activation. Regarding the structure-activity relationships for the five acylphloroglucinol compounds, our results demonstrated that the functional butanonyl, methoxy, and hydroxy groups in butyryl-3-methylphloroglucinol play important roles in antiplatelet activity. The findings indicate that acylphloroglucinols, including butyryl-3-methylphloroglucinol from D. crassirhizom, possess an antiplatelet activity, supporting the use of this species for antiplatelet remedies.

Comparative anti-thrombotic activity and haemorrhagic adverse effect of nattokinase and tissue-type plasminogen activator

Anti-thrombotic activity and safety of nattokinase, an enzyme produced by Bacillus subtilis during soybean fermentation, were investigated in comparison with tissue-type plasminogen activator (t-PA). Carotid arterial thrombosis was produced with a FeCl₃-soaked paper, followed by intravenous injection of nattokinase or t-PA. Nattokinase and t-PA delayed thrombus formation, near-fully (> 90%) inhibiting at 75 and 8.5 mg/kg, respectively. As adverse effects, t-PA induced petechial haemorrhage at 10 mg/kg in the lungs and thymus, and extensive bleeding at 20 mg/kg. Nattokinase also caused pulmonary haemorrhage from 300 mg/kg. Collectively, the standard safety margins (SSMs) for t-PA and nattokinase were calculated to be 1.2 and 4.0, respectively. Combinational treatment with dexamethasone (2 mg/kg) increased the efficacy and safety of t-PA and nattokinase, widening their SSMs to 2.4 and 8.0, respectively. The results indicate that nattokinase delayed thrombus formation and dissolved thrombi, and that nattokinase could be a good candidate anti-thrombotic agent with relatively-low haemorrhagic risk.

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

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

Antiplatelet action of indirubin-3'-monoxime through suppression of glycoprotein VI-mediated signal transduction: a possible role for ERK signaling in platelets

We investigated the antiplatelet activity of indirubin-3'-monoxime (I3O) and the underlying mechanisms. In a rat carotid artery injury model, oral administration (20 mg/kg/day) of I3O for 3 days significantly prolonged occlusion time, and ADP- and collagen-induced platelet aggregation. In washed platelets in vitro, I3O potently inhibited collagen-induced platelet aggregation by suppressing phospholipase Cγ2 (PLCγ2) phosphorylation, subsequently blocking diacylglycerol and arachidonic acid (AA) formation, P-selectin secretion and the production of thromboxane B2. Platelet aggregation induced by phorbol-12-myristate 13-acetate, a protein kinase C (PKC) activator, was inhibited by I3O. Both I3O and U0126, an extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor, markedly reduced collagen-induced phosphorylation of ERK1/2 and p47, resulting in the blockade of cyclooxygenase (COX)-mediated AA metabolite production in AA-treated platelets. I3O suppressed phosphorylation of JNK, p38, GSK-3β, and AKT. I3O inhibited glycoprotein VI (GPVI), as a collagen receptor, by suppressing the phosphorylation of tyrosine kinase Syk of GPVI and the phosphorylation of PLCγ2 and ERK1/2 stimulated by convulxin, as a specific stimulator. Our results indicate that an antiplatelet effect of I3O is due to the suppression of GPVI-mediated signaling pathways. In collagen-stimulated platelets, ERK1/2 phosphorylation is adenylyl cyclase-dependent and leads to the modulation of PKC-p47 signaling and COX-1-mediated AA-metabolic pathways.

Perilla oil improves blood flow through inhibition of platelet aggregation and thrombus formation

The inhibitory effects of perilla oil on the platelet aggregation in vitro and thrombosis in vivo were investigated in comparison with aspirin, a well-known blood flow enhancer. Rabbit platelet-rich plasma was incubated with perilla oil and aggregation inducers collagen or thrombin, and the platelet aggregation rate was analyzed. Perilla oil significantly inhibited both the collagen- and thrombin-induced platelet aggregations, in which the thromboxane B₂ formation from collagen-activated platelets were reduced in a concentration-dependent manner. Rats were administered once daily by gavage with perilla oil for 1 week, carotid arterial thrombosis was induced by applying 35% FeCl₃-soaked filter paper for 10 min, and the blood flow was monitored with a laser Doppler probe. Perilla oil delayed the FeCl₃-induced arterial occlusion in a dose-dependent manner, doubling the occlusion time at 0.5 mL/kg. In addition, a high dose (2 mL/kg) of perilla oil greatly prevented the occlusion, comparable to the effect of aspirin (30 mg/kg). The results indicate that perilla oil inhibit platelet aggregation by blocking thromboxane formation, and thereby delay thrombosis following oxidative arterial wall injury. Therefore, it is proposed that perilla oil could be a good candidate without adverse effects for the improvement of blood flow.

Nattokinase improves blood flow by inhibiting platelet aggregation and thrombus formation

The effects of nattokinase on the in vitro platelet aggregation and in vivo thrombosis were investigated in comparison with aspirin. Rabbit platelet-rich plasma was incubated with nattokinase and aggregation inducers collagen and thrombin, and the platelet aggregation rate was analyzed. Nattokinase significantly inhibited both the collagen- and thrombin-induced platelet aggregations. Nattokinase also reduced thromboxane B2 formation from collagen-activated platelets in a concentration-dependent manner. Rats were orally administered with nattokinase for 1 week, and their carotid arteries were exposed. Arterial thrombosis was induced by applying 35% FeCl3-soaked filter paper for 10 min, and the blood flow was monitored with a laser Doppler probe. Nattokinase delayed the FeCl3-induced arterial occlusion in a dose-dependent manner, doubling the occlusion time at 160 mg/kg. In addition, a high dose (500 mg/kg) of nattokinase fully prevented the occlusion, as achieved with aspirin (30 mg/kg). The results indicate that nattokinase extracted from fermented soybean inhibit platelet aggregation by blocking thromboxane formation, and thereby delay thrombosis following oxidative arterial wall injury. Therefore, it is suggested that nattokinase could be a good candidate without adverse effects for the improvement of blood flow.

Lack of antiapoptotic effects of antiplatelet drug, aspirin and clopidogrel, and antioxidant, MCI-186, against focal ischemic brain damage in rats

OBJECTIVES

This study evaluated the antiapoptotic effect of antiplatelet drugs, aspirin and clopidogrel, and the antioxidant drug, MCI-186, against focal cerebral ischemic rat brain damage.

METHODS

Cerebral ischemia was mechanically induced by 2-hour occlusion of the left middle cerebral artery (MCA) using an intraluminal filament followed by 24-hour reperfusion.

RESULTS

The cerebral infarct size was little affected by oral administration of 300 mg/kg aspirin, 30 mg/kg clopidogrel or 100 mg/kg MCI-186, but was significantly reduced by 30 mg/kg cilostazol. However, intravenous administration of 10 mg/kg MCI-186 suppressed the infarct size. DNA fragmentation observed in the cortical tissues corresponding to the penumbral zone was not suppressed by aspirin, clopidogrel or MCI-186, but was significantly suppressed by cilostazol. Increased phosphorylation of phosphatase and tensin homolog deleted from chromosome 10 (PTEN) and Bax protein, and decreased Akt/cyclic AMP response element binding protein (CREB) phosphorylation, including Bcl-2 protein in the vehicle-treated group were not affected by treatment with aspirin, clopidogrel and MCI-186, whereas those effects were reversed by cilostazol.

CONCLUSION

Thus, it is suggested that antiplatelet drugs, aspirin and clopidogrel, and antioxidant drug, MCI-186, showed little antiapoptotic effect in contrast to cilostazol.

Antithrombotic and antiplatelet activities of Soshiho-tang extract

Background

Soshiho-tang (SH; Chinese name, Xiao-Chai-Hu-Tang; Japanese name, Shosaiko-to) is a traditional Korean, Chinese, and Japanese medicine, which has been used to treat various conditions, including hepatitis, liver cirrhosis, and chronic and acute liver disease. SH consists of seven herbal components, of which Scutellaria baicalensis Georgi and Zingiber officinale Roscoe, are reported to have antithrombotic and antiplatelet activities. We investigated the antithrombotic activity of SH, including S. baicalensis and Z. officinale, as an integrative therapy.

Methods

To identify the antithrombotic activity of SH, we used a FeCl₃-induced thrombus formation model. The mechanism of SH-mediated antithrombotic activity was assessed by determining platelet aggregation and coagulation times ex vivo, washed platelet aggregation, serotonin secretion, and thromboxane B₂ formation.

Results

SH prolonged the occlusion time of thrombus formation when applied in a FeCl₃-induced thrombus formation model. SH also inhibited collagen-induced platelet aggregation ex vivo in a concentration-dependent manner; however, it did not affect coagulation. Hence, to identify the antiplatelet effect of SH, we investigated washed platelet aggregations in vitro. SH significantly inhibited various agonist-induced platelet aggregations, and it completely inhibited serotonin secretion and thromboxane B₂ formation.

Conclusions

The findings suggest that SH inhibited FeCl₃-induced thrombus formation through antiplatelet activity, including inhibition of platelet aggregation, and serotonin and TXB₂ production. Thus, SH may be useful as an integrative herbal formula for the treatment of thrombosis.

Anti-platelet activity of diacetylated obovatol through regulating cyclooxygenase and lipoxygenase activities

Obovatol has been reported biological activities such as muscle relaxative, anti-gastric ulcer, anti-allergic and anti-bacterial activities. The present study was undertaken to investigate the effect of diacetylated obovatol, an obovatol derivative, on rabbit platelet aggregation, and their possible molecular mechanisms. Effects of diacetylated obovatol on platelet activation including aggregation and serotonin secretion were examined. In addition, we investigated the effect of diacetylated obovatol on archidonic acid and metabolites liberation and intracellular calcium mobilization. Diacetylated obovatol concentration-dependently inhibited the washed rabbit platelet aggregation induced by collagen and arachidonic acid, suggesting that diacetylated obovatol may selectively inhibits collagen- and arachidonic acid-mediated signal transduction. In accordance with these results, diacetylated obovatol showed a concentration-dependent decrease in cytosolic Ca(2+) mobilization and serotonin secretion. However, diacetylated obovatol did not inhibit arachidonic acid liberation; on the other hand, diacetylated obovatol inhibited the formation of arachidonic acid metabolites such as thromboxane A(2), prostaglandin D(2) and 12-HETE through interfering with cyclooxygenase (COX)-1 and lipoxygenase (LOX) activities. The results demonstrated that diacetylated obovatol has antiplatelet activities through inhibition of COX-1 and LOX activities.

Protective effects of cilostazol against transient focal cerebral ischemia and chronic cerebral hypoperfusion injury

Cilostazol increases intracellular cyclic adenosine monophosphate (cyclic AMP) levels by inhibiting type III phosphodiesterase. It was approved by the Food and Drug Administration for the treatment of intermittent claudication. Its principal actions include inhibition of platelet aggregation, antithrombotic action in cerebral ischemia, and vasodilation, mediated by increased cyclic AMP levels. In a multicenter, randomized, placebo-controlled, double-blind clinical trial, cilostazol has been shown to protect patients from recurrent cerebral infarction. It has been recently suggested that cilastozol could be useful in the treatment of transient focal cerebral ischemic injury. Beneficial effects of cilostazol in cerebral ischemic infarction and edema formation has been confirmed in rats by the magnetic resonance imaging (MRI). The preventive effect was ascribed to cAMP-dependent protein kinase (PKA)-coupled maxi-K channel activation with additional antioxidant and poly(adenosine diphosphate [ADP]-ribose) polymerase inhibitory actions. Most recently, cilostazol has been shown to prevent vacuolation and rarefaction in the white matter of the rats subjected to chronic cerebral hypoperfusion in association with suppression of astrocyte and microglial activation. Taken together, recent experimental studies with cilostazol showed promising results in cerebral ischemia and chronic cerebral hypoperfusion.

Clopidogrel and Bleeding after General Surgery Procedures

Although many studies in the cardiothoracic literature exist about the relationship between clopidogrel and postoperative bleeding, there is scarce data in the general surgery literature. We assessed whether there are increased bleeding complications, morbidity, mortality, and resource utilization in patients who are on clopidogrel (Plavix®) within 1 week before undergoing a general surgery procedure. Fifty consecutive patient charts were retrospectively reviewed after identifying patients who had pharmacy orders for clopidogrel and who underwent a general surgery procedure between 2003 and 2007. Patients who took clopidogrel within 6 days before surgery (group I, n = 28) were compared with patients who stopped clopidogrel for 7 days or more (group II, n = 22). A larger percentage of patients who took their last dose of clopidogrel within 1 week of surgery (21.4% vs 9.5%) had significant bleeding after surgery requiring blood transfusion. However, there were no significant differences between the groups in operative or postoperative blood transfusions ( P = 0.12, 0.53), decreases in hematocrit ( P = 0.21), hospital stay ( P = 0.09), intensive care unit stay ( P = 0.41), late complications ( P = 0.45), or mortality ( P = 0.42). Although our cohort is limited in size, these results suggest that in the case of a nonelective general surgery procedure where outcomes depend on timely surgery, clopidogrel taken within 6 days before surgery should not be a reason to delay surgery. However, careful attention must be paid to meticulous hemostasis, and platelets must be readily available for transfusion in the operating room.

Characterization of ischemic events and use of prescription antiplatelet and anticoagulant agents after stroke or transient ischemic attack

Stroke patients are at risk for subsequent ischemic events; yet preventive therapy is often underused. An analysis was performed to determine the rate of secondary ischemic events and use of prescription antiplatelets or anticoagulants after ischemic stroke or transient ischemic attack (TIA). Patients age 25 years or older with a medical claim for stroke or TIA between July 1, 1998 and September 30, 1999 were identified from a managed care database. Patients sustaining a stroke or TIA within 6 months before the index event were excluded. Patients were categorized as hospitalized stroke, nonhospitalized stroke, or TIA and were followed for 24 months for a secondary stroke, TIA, or acute myocardial infarction (AMI). Use of prescription antiplatelet or anticoagulant agents was determined for each subgroup. Over 2 years, subsequent stroke occurred in 5.8% of patients, TIA occurred in 3.8%, and AMI occurred in 4.9%. Death occurred in 32.3% during follow-up. Hospitalized stroke patients were the subgroup at highest risk, with a 7.6% stroke rate and a 45.4% death rate within 2 years. Prescription antiplatelet or warfarin therapy was given in 45.7% of hospitalized stroke cases, 29.5% of nonhospitalized stroke cases, and 39.2% of TIA cases. Against the background of current treatment, patients who suffer a stroke or TIA are at high risk of death and a subsequent stroke within 2 years. These outcomes highlight the importance of effective secondary stroke prevention efforts for those suffering acute stroke, whether or not they are hospitalized.

Progress in 5H[1]benzopyrano[4,3-d]pyrimidin-5-amine series: 2-methoxy derivatives effective as antiplatelet agents with analgesic activity

A series of 2-methoxy-5H[1]benzopyrano[4,3-d]pyrimidin-5-amines were prepared and screened for their in vitro antiplatelet activity inducing the aggregation by ADP, arachidonic acid (AA) and collagen. In vivo experiments were performed in order to evaluate their antiphlogistic, analgesic and antipyretic activities. Title compounds showed antiplatelet activity in aggregation AA or collagen-induced, and a good analgesic activity without any gastric toxicity. Comparison with a number of analogue benzopyrano[4,3-d]pyrimidine derivatives and some SAR consideration were reported.

Vascular dementia revisited: diagnosis, pathogenesis, treatment, and prevention

VaD is the second most common cause of dementia in the elderly after AD. VaD is defined as the loss of cognitive function resulting from ischemic, ischemic-hypoxic, or hemorrhagic brain lesions as a result of CVD and cardiovascular pathologic changes. Diagnosis requires (1) cognitive loss (often predominantly subcortical), (2) vascular brain lesions demonstrated by imaging, and (3) exclusion of other causes of dementia, such as AD. VaD is excluded by brain imaging showing no evidence of vascular lesions. VaD may be caused by multiple strokes (MID or poststroke dementia) but also by single strategic strokes, multiple lacunes, and hypoperfusive lesions such as border zone infarcts and ischemic periventricular leukoencephalopathy (Binswanger's disease). Primary and secondary prevention of stroke and cardiovascular disease decreases the burden of VaD. Genetic advice is needed in patients with familial forms, such as CADASIL. Treatment involves control of risk factors (i.e., hypertension, diabetes, smoking, hyperfibrinogenemia, hyperhomocystinemia, orthostatic hypotension, cardiac arrhythmias). Anticholinergic medications used for AD are also useful in VaD, and atypical antipsychotic agents and antidepressants (e.g., selective serotonin reuptake inhibitors) may be required in some patients.